diff --git a/src/ai/ai_gui.cpp b/src/ai/ai_gui.cpp
index 33286f500e..beeed22bc2 100644
--- a/src/ai/ai_gui.cpp
+++ b/src/ai/ai_gui.cpp
@@ -314,7 +314,7 @@ struct AISettingsWindow : public Window {
 		if (_game_mode == GM_MENU) {
 			if (_settings_newgame.difficulty.diff_level != 3) {
 				_settings_newgame.difficulty.diff_level = 3;
-				ShowErrorMessage(STR_WARNING_DIFFICULTY_TO_CUSTOM, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_WARNING_DIFFICULTY_TO_CUSTOM, INVALID_STRING_ID, WL_WARNING);
 			}
 		} else if (_settings_game.difficulty.diff_level != 3) {
 			IConsoleSetSetting("difficulty.diff_level", 3);
@@ -632,7 +632,7 @@ struct AIConfigWindow : public Window {
 
 			case AIC_WIDGET_CONTENT_DOWNLOAD:
 				if (!_network_available) {
-					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, WL_ERROR);
 				} else {
 #if defined(ENABLE_NETWORK)
 					ShowNetworkContentListWindow(NULL, CONTENT_TYPE_AI);
@@ -1013,6 +1013,6 @@ void ShowAIDebugWindow(CompanyID show_company)
 		if (w == NULL) w = new AIDebugWindow(&_ai_debug_desc, 0);
 		if (show_company != INVALID_COMPANY) w->ChangeToAI(show_company);
 	} else {
-		ShowErrorMessage(STR_ERROR_AI_DEBUG_SERVER_ONLY, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_ERROR_AI_DEBUG_SERVER_ONLY, INVALID_STRING_ID, WL_INFO);
 	}
 }
diff --git a/src/ai/ai_gui.hpp b/src/ai/ai_gui.hpp
index 254e2955cb..e766816368 100644
--- a/src/ai/ai_gui.hpp
+++ b/src/ai/ai_gui.hpp
@@ -22,7 +22,7 @@ void ShowAIConfigWindow();
 
 static inline void ShowAIConfigWindow()
 {
-	ShowErrorMessage(STR_ERROR_NO_AI, STR_ERROR_NO_AI_SUB, 0, 0);
+	ShowErrorMessage(STR_ERROR_NO_AI, STR_ERROR_NO_AI_SUB, WL_INFO);
 }
 static inline void ShowAIDebugWindow(CompanyID show_company = INVALID_COMPANY) {ShowAIConfigWindow();}
 #endif /* ENABLE_AI */
diff --git a/src/ai/ai_instance.cpp b/src/ai/ai_instance.cpp
index 95250fd6c0..41ec1c85ef 100644
--- a/src/ai/ai_instance.cpp
+++ b/src/ai/ai_instance.cpp
@@ -297,7 +297,7 @@ void AIInstance::Died()
 
 	const AIInfo *info = AIConfig::GetConfig(_current_company)->GetInfo();
 	if (info != NULL) {
-		ShowErrorMessage(STR_ERROR_AI_PLEASE_REPORT_CRASH, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_ERROR_AI_PLEASE_REPORT_CRASH, INVALID_STRING_ID, WL_WARNING);
 
 		if (info->GetURL() != NULL) {
 			AILog::Info("Please report the error to the following URL:");
diff --git a/src/bridge_gui.cpp b/src/bridge_gui.cpp
index 98d47c492f..cccfbeddeb 100644
--- a/src/bridge_gui.cpp
+++ b/src/bridge_gui.cpp
@@ -412,6 +412,6 @@ void ShowBuildBridgeWindow(TileIndex start, TileIndex end, TransportType transpo
 		new BuildBridgeWindow(&_build_bridge_desc, start, end, type, bl);
 	} else {
 		delete bl;
-		ShowErrorMessage(STR_ERROR_CAN_T_BUILD_BRIDGE_HERE, errmsg, TileX(end) * TILE_SIZE, TileY(end) * TILE_SIZE);
+		ShowErrorMessage(STR_ERROR_CAN_T_BUILD_BRIDGE_HERE, errmsg, WL_INFO, TileX(end) * TILE_SIZE, TileY(end) * TILE_SIZE);
 	}
 }
diff --git a/src/command.cpp b/src/command.cpp
index 430f9d2ebc..eb992a2d2d 100644
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -511,7 +511,7 @@ bool DoCommandP(TileIndex tile, uint32 p1, uint32 p2, uint32 cmd, CommandCallbac
 		/* Only show the error when it's for us. */
 		StringID error_part1 = GB(cmd, 16, 16);
 		if (estimate_only || (IsLocalCompany() && error_part1 != 0 && my_cmd)) {
-			ShowErrorMessage(error_part1, _error_message, x, y);
+			ShowErrorMessage(error_part1, _error_message, WL_INFO, x, y);
 		}
 	} else if (estimate_only) {
 		ShowEstimatedCostOrIncome(res.GetCost(), x, y);
diff --git a/src/company_gui.cpp b/src/company_gui.cpp
index ce9242c2b3..c4e7b5e512 100644
--- a/src/company_gui.cpp
+++ b/src/company_gui.cpp
@@ -1418,7 +1418,7 @@ public:
 			case SCMFW_WIDGET_LOAD:
 				this->face = _company_manager_face;
 				ScaleAllCompanyManagerFaceBits(this->face);
-				ShowErrorMessage(STR_FACE_LOAD_DONE, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_FACE_LOAD_DONE, INVALID_STRING_ID, WL_INFO);
 				this->UpdateData();
 				this->SetDirty();
 				break;
@@ -1432,7 +1432,7 @@ public:
 			/* Save button */
 			case SCMFW_WIDGET_SAVE:
 				_company_manager_face = this->face;
-				ShowErrorMessage(STR_FACE_SAVE_DONE, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_FACE_SAVE_DONE, INVALID_STRING_ID, WL_INFO);
 				break;
 
 			/* Toggle gender (male/female) button */
@@ -1509,11 +1509,11 @@ public:
 		if (!StrEmpty(str)) {
 			this->face = strtoul(str, NULL, 10);
 			ScaleAllCompanyManagerFaceBits(this->face);
-			ShowErrorMessage(STR_FACE_FACECODE_SET, INVALID_STRING_ID, 0, 0);
+			ShowErrorMessage(STR_FACE_FACECODE_SET, INVALID_STRING_ID, WL_INFO);
 			this->UpdateData();
 			this->SetDirty();
 		} else {
-			ShowErrorMessage(STR_FACE_FACECODE_ERR, INVALID_STRING_ID, 0, 0);
+			ShowErrorMessage(STR_FACE_FACECODE_ERR, INVALID_STRING_ID, WL_INFO);
 		}
 	}
 };
diff --git a/src/gui.h b/src/gui.h
index 11e501f3d0..f6a0e14df3 100644
--- a/src/gui.h
+++ b/src/gui.h
@@ -52,7 +52,16 @@ void ShowIndustryDirectory();
 void ShowSubsidiesList();
 
 void ShowEstimatedCostOrIncome(Money cost, int x, int y);
-void ShowErrorMessage(StringID summary_msg, StringID detailed_msg, int x, int y, bool no_timeout = false);
+
+/** Message severity/type */
+enum WarningLevel {
+	WL_INFO,     ///< Used for DoCommand-like (and some nonfatal AI GUI) errors/information
+	WL_WARNING,  ///< Other information
+	WL_ERROR,    ///< Errors (eg. saving/loading failed)
+	WL_CRITICAL, ///< Critical errors, the MessageBox is shown in all cases
+};
+
+void ShowErrorMessage(StringID summary_msg, StringID detailed_msg, WarningLevel wl, int x = 0, int y = 0);
 
 void ShowExtraViewPortWindow(TileIndex tile = INVALID_TILE);
 
diff --git a/src/heightmap.cpp b/src/heightmap.cpp
index 68a1ecffb6..9b72a873fe 100644
--- a/src/heightmap.cpp
+++ b/src/heightmap.cpp
@@ -107,20 +107,20 @@ static bool ReadHeightmapPNG(char *filename, uint *x, uint *y, byte **map)
 
 	fp = FioFOpenFile(filename, "rb");
 	if (fp == NULL) {
-		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_FILE_NOT_FOUND, 0, 0);
+		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_FILE_NOT_FOUND, WL_ERROR);
 		return false;
 	}
 
 	png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
 	if (png_ptr == NULL) {
-		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_MISC, 0, 0);
+		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_MISC, WL_ERROR);
 		fclose(fp);
 		return false;
 	}
 
 	info_ptr = png_create_info_struct(png_ptr);
 	if (info_ptr == NULL || setjmp(png_jmpbuf(png_ptr))) {
-		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_MISC, 0, 0);
+		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_MISC, WL_ERROR);
 		fclose(fp);
 		png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
 		return false;
@@ -136,7 +136,7 @@ static bool ReadHeightmapPNG(char *filename, uint *x, uint *y, byte **map)
 	/* Maps of wrong colour-depth are not used.
 	 * (this should have been taken care of by stripping alpha and 16-bit samples on load) */
 	if ((png_get_channels(png_ptr, info_ptr) != 1) && (png_get_channels(png_ptr, info_ptr) != 3) && (png_get_bit_depth(png_ptr, info_ptr) != 8)) {
-		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_IMAGE_TYPE, 0, 0);
+		ShowErrorMessage(STR_ERROR_PNGMAP, STR_ERROR_PNGMAP_IMAGE_TYPE, WL_ERROR);
 		fclose(fp);
 		png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
 		return false;
@@ -230,14 +230,14 @@ static bool ReadHeightmapBMP(char *filename, uint *x, uint *y, byte **map)
 
 	f = FioFOpenFile(filename, "rb");
 	if (f == NULL) {
-		ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_PNGMAP_FILE_NOT_FOUND, 0, 0);
+		ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_PNGMAP_FILE_NOT_FOUND, WL_ERROR);
 		return false;
 	}
 
 	BmpInitializeBuffer(&buffer, f);
 
 	if (!BmpReadHeader(&buffer, &info, &data)) {
-		ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_BMPMAP_IMAGE_TYPE, 0, 0);
+		ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_BMPMAP_IMAGE_TYPE, WL_ERROR);
 		fclose(f);
 		BmpDestroyData(&data);
 		return false;
@@ -245,7 +245,7 @@ static bool ReadHeightmapBMP(char *filename, uint *x, uint *y, byte **map)
 
 	if (map != NULL) {
 		if (!BmpReadBitmap(&buffer, &info, &data)) {
-			ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_BMPMAP_IMAGE_TYPE, 0, 0);
+			ShowErrorMessage(STR_ERROR_BMPMAP, STR_ERROR_BMPMAP_IMAGE_TYPE, WL_ERROR);
 			fclose(f);
 			BmpDestroyData(&data);
 			return false;
diff --git a/src/industry_gui.cpp b/src/industry_gui.cpp
index 56ceeb81b3..0380ebb209 100644
--- a/src/industry_gui.cpp
+++ b/src/industry_gui.cpp
@@ -423,7 +423,7 @@ public:
 					this->HandleButtonClick(DPIW_FUND_WIDGET);
 
 					if (Town::GetNumItems() == 0) {
-						ShowErrorMessage(STR_ERROR_CAN_T_GENERATE_INDUSTRIES, STR_ERROR_MUST_FOUND_TOWN_FIRST, 0, 0);
+						ShowErrorMessage(STR_ERROR_CAN_T_GENERATE_INDUSTRIES, STR_ERROR_MUST_FOUND_TOWN_FIRST, WL_INFO);
 					} else {
 						extern void GenerateIndustries();
 						_generating_world = true;
@@ -458,7 +458,7 @@ public:
 			/* Show error if no town exists at all */
 			if (Town::GetNumItems() == 0) {
 				SetDParam(0, indsp->name);
-				ShowErrorMessage(STR_ERROR_CAN_T_BUILD_HERE, STR_ERROR_MUST_FOUND_TOWN_FIRST, pt.x, pt.y);
+				ShowErrorMessage(STR_ERROR_CAN_T_BUILD_HERE, STR_ERROR_MUST_FOUND_TOWN_FIRST, WL_INFO, pt.x, pt.y);
 				return;
 			}
 
@@ -468,7 +468,7 @@ public:
 			success = DoCommandP(tile, (InteractiveRandomRange(indsp->num_table) << 8) | this->selected_type, seed, CMD_BUILD_INDUSTRY | CMD_MSG(STR_ERROR_CAN_T_CONSTRUCT_THIS_INDUSTRY));
 			if (!success) {
 				SetDParam(0, indsp->name);
-				ShowErrorMessage(STR_ERROR_CAN_T_BUILD_HERE, _error_message, pt.x, pt.y);
+				ShowErrorMessage(STR_ERROR_CAN_T_BUILD_HERE, _error_message, WL_INFO, pt.x, pt.y);
 			}
 
 			_ignore_restrictions = false;
diff --git a/src/intro_gui.cpp b/src/intro_gui.cpp
index f65d68f9f9..5cb4a38907 100644
--- a/src/intro_gui.cpp
+++ b/src/intro_gui.cpp
@@ -121,7 +121,7 @@ struct SelectGameWindow : public Window {
 
 			case SGI_PLAY_NETWORK:
 				if (!_network_available) {
-					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, WL_ERROR);
 				} else {
 					ShowNetworkGameWindow();
 				}
@@ -140,7 +140,7 @@ struct SelectGameWindow : public Window {
 			case SGI_GRF_SETTINGS:    ShowNewGRFSettings(true, true, false, &_grfconfig_newgame); break;
 			case SGI_CONTENT_DOWNLOAD:
 				if (!_network_available) {
-					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, WL_ERROR);
 				} else {
 					ShowNetworkContentListWindow();
 				}
diff --git a/src/misc_gui.cpp b/src/misc_gui.cpp
index c456394f61..0e9a751623 100644
--- a/src/misc_gui.cpp
+++ b/src/misc_gui.cpp
@@ -33,6 +33,7 @@
 #include "window_func.h"
 #include "tilehighlight_func.h"
 #include "querystring_gui.h"
+#include "console_func.h"
 #include "core/geometry_func.hpp"
 
 #include "table/strings.h"
@@ -690,14 +691,16 @@ public:
  * Display an error message in a window.
  * @param summary_msg  General error message showed in first line. Must be valid.
  * @param detailed_msg Detailed error message showed in second line. Can be INVALID_STRING_ID.
+ * @param wl           Message severity
  * @param x            World X position (TileVirtX) of the error location. Set both x and y to 0 to just center the message when there is no related error tile.
  * @param y            World Y position (TileVirtY) of the error location. Set both x and y to 0 to just center the message when there is no related error tile.
- * @param no_timeout   Set to true, if the message is that important that it should not close automatically after some time.
  */
-void ShowErrorMessage(StringID summary_msg, StringID detailed_msg, int x, int y, bool no_timeout)
+void ShowErrorMessage(StringID summary_msg, StringID detailed_msg, WarningLevel wl, int x, int y)
 {
 	DeleteWindowById(WC_ERRMSG, 0);
 
+	bool no_timeout = wl == WL_CRITICAL;
+
 	if (_settings_client.gui.errmsg_duration == 0 && !no_timeout) return;
 
 	if (summary_msg == STR_NULL) summary_msg = STR_EMPTY;
@@ -716,7 +719,7 @@ void ShowEstimatedCostOrIncome(Money cost, int x, int y)
 		msg = STR_MESSAGE_ESTIMATED_INCOME;
 	}
 	SetDParam(0, cost);
-	ShowErrorMessage(msg, INVALID_STRING_ID, x, y);
+	ShowErrorMessage(msg, INVALID_STRING_ID, WL_INFO, x, y);
 }
 
 void ShowCostOrIncomeAnimation(int x, int y, int z, Money cost)
@@ -1874,7 +1877,7 @@ public:
 
 			case SLWW_CONTENT_DOWNLOAD:
 				if (!_network_available) {
-					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, WL_ERROR);
 				} else {
 #if defined(ENABLE_NETWORK)
 					switch (_saveload_mode) {
@@ -1922,7 +1925,7 @@ public:
 
 		if (this->IsWidgetLowered(SLWW_DELETE_SELECTION)) { // Delete button clicked
 			if (!FiosDelete(this->text.buf)) {
-				ShowErrorMessage(STR_ERROR_UNABLE_TO_DELETE_FILE, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_ERROR_UNABLE_TO_DELETE_FILE, INVALID_STRING_ID, WL_ERROR);
 			} else {
 				BuildFileList();
 				/* Reset file name to current date on successful delete */
diff --git a/src/music_gui.cpp b/src/music_gui.cpp
index 4ede5801ea..5907da582a 100644
--- a/src/music_gui.cpp
+++ b/src/music_gui.cpp
@@ -803,6 +803,6 @@ static const WindowDesc _music_window_desc(
 
 void ShowMusicWindow()
 {
-	if (BaseMusic::GetUsedSet()->num_available == 0) ShowErrorMessage(STR_ERROR_NO_SONGS, INVALID_STRING_ID, 0, 0);
+	if (BaseMusic::GetUsedSet()->num_available == 0) ShowErrorMessage(STR_ERROR_NO_SONGS, INVALID_STRING_ID, WL_WARNING);
 	AllocateWindowDescFront<MusicWindow>(&_music_window_desc, 0);
 }
diff --git a/src/network/network_content.cpp b/src/network/network_content.cpp
index b5177d6ada..d5ed2a3747 100644
--- a/src/network/network_content.cpp
+++ b/src/network/network_content.cpp
@@ -422,7 +422,7 @@ DEF_CONTENT_RECEIVE_COMMAND(Client, PACKET_CONTENT_SERVER_CONTENT)
 		size_t toRead = (size_t)(p->size - p->pos);
 		if (fwrite(p->buffer + p->pos, 1, toRead, this->curFile) != toRead) {
 			DeleteWindowById(WC_NETWORK_STATUS_WINDOW, 0);
-			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD_FILE_NOT_WRITABLE, STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD, 0, 0);
+			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD_FILE_NOT_WRITABLE, STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD, WL_ERROR);
 			this->Close();
 			fclose(this->curFile);
 			this->curFile = NULL;
@@ -456,7 +456,7 @@ bool ClientNetworkContentSocketHandler::BeforeDownload()
 		if (filename == NULL) {
 			/* Unless that fails ofcourse... */
 			DeleteWindowById(WC_NETWORK_STATUS_WINDOW, 0);
-			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD_FILE_NOT_WRITABLE, STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD, 0, 0);
+			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD_FILE_NOT_WRITABLE, STR_CONTENT_ERROR_COULD_NOT_DOWNLOAD, WL_ERROR);
 			return false;
 		}
 
@@ -483,7 +483,7 @@ void ClientNetworkContentSocketHandler::AfterDownload()
 
 		this->OnDownloadComplete(this->curInfo->id);
 	} else {
-		ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_EXTRACT, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_EXTRACT, INVALID_STRING_ID, WL_ERROR);
 	}
 }
 
diff --git a/src/network/network_content_gui.cpp b/src/network/network_content_gui.cpp
index bb77aea6d5..a25a5ad4ab 100644
--- a/src/network/network_content_gui.cpp
+++ b/src/network/network_content_gui.cpp
@@ -742,7 +742,7 @@ public:
 	virtual void OnConnect(bool success)
 	{
 		if (!success) {
-			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_CONNECT, INVALID_STRING_ID, 0, 0);
+			ShowErrorMessage(STR_CONTENT_ERROR_COULD_NOT_CONNECT, INVALID_STRING_ID, WL_ERROR);
 			delete this;
 			return;
 		}
@@ -886,7 +886,7 @@ void ShowNetworkContentListWindow(ContentVector *cv, ContentType type)
 	DeleteWindowById(WC_NETWORK_WINDOW, 1);
 	new NetworkContentListWindow(&_network_content_list_desc, cv != NULL);
 #else
-	ShowErrorMessage(STR_CONTENT_NO_ZLIB, STR_CONTENT_NO_ZLIB_SUB, 0, 0);
+	ShowErrorMessage(STR_CONTENT_NO_ZLIB, STR_CONTENT_NO_ZLIB_SUB, WL_ERROR);
 	/* Connection failed... clean up the mess */
 	if (cv != NULL) {
 		for (ContentIterator iter = cv->Begin(); iter != cv->End(); iter++) delete *iter;
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index 96c3d7beac..23fafad3c5 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -44,7 +44,7 @@ void ShowNewGRFError()
 		for (uint i = 0; i < c->error->num_params; i++) {
 			SetDParam(6 + i, c->error->param_value[i]);
 		}
-		ShowErrorMessage(STR_NEWGRF_ERROR_FATAL_POPUP, INVALID_STRING_ID, 0, 0, true);
+		ShowErrorMessage(STR_NEWGRF_ERROR_FATAL_POPUP, INVALID_STRING_ID, WL_CRITICAL);
 		break;
 	}
 }
@@ -370,7 +370,7 @@ public:
 					/* Find last entry in the list, checking for duplicate grfid on the way */
 					for (list = this->list; *list != NULL; list = &(*list)->next) {
 						if ((*list)->grfid == src->grfid) {
-							ShowErrorMessage(STR_NEWGRF_DUPLICATE_GRFID, INVALID_STRING_ID, 0, 0);
+							ShowErrorMessage(STR_NEWGRF_DUPLICATE_GRFID, INVALID_STRING_ID, WL_INFO);
 							return;
 						}
 					}
@@ -850,7 +850,7 @@ struct NewGRFWindow : public Window {
 
 			case SNGRFS_CONTENT_DOWNLOAD:
 				if (!_network_available) {
-					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_NETWORK_ERROR_NOTAVAILABLE, INVALID_STRING_ID, WL_ERROR);
 				} else {
 #if defined(ENABLE_NETWORK)
 				/* Only show the things in the current list, or everything when nothing's selected */
diff --git a/src/newgrf_industries.cpp b/src/newgrf_industries.cpp
index 905e66739e..ceff4923f4 100644
--- a/src/newgrf_industries.cpp
+++ b/src/newgrf_industries.cpp
@@ -537,7 +537,7 @@ void IndustryProductionCallback(Industry *ind, int reason)
 			/* display error message */
 			SetDParamStr(0, spec->grf_prop.grffile->filename);
 			SetDParam(1, spec->name);
-			ShowErrorMessage(STR_NEWGRF_BUGGY, STR_NEWGRF_BUGGY_ENDLESS_PRODUCTION_CALLBACK, 0, 0);
+			ShowErrorMessage(STR_NEWGRF_BUGGY, STR_NEWGRF_BUGGY_ENDLESS_PRODUCTION_CALLBACK, WL_WARNING);
 
 			/* abort the function early, this error isn't critical and will allow the game to continue to run */
 			break;
diff --git a/src/openttd.cpp b/src/openttd.cpp
index a1559592ee..869cb6f817 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -870,7 +870,7 @@ static void StartScenario()
 	if (_file_to_saveload.mode == SL_INVALID) {
 		DEBUG(sl, 0, "Savegame is obsolete or invalid format: '%s'", _file_to_saveload.name);
 		SetDParamStr(0, GetSaveLoadErrorString());
-		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 		_game_mode = GM_MENU;
 		return;
 	}
@@ -886,7 +886,7 @@ static void StartScenario()
 	if (SaveOrLoad(_file_to_saveload.name, _file_to_saveload.mode, SCENARIO_DIR) != SL_OK) {
 		LoadIntroGame();
 		SetDParamStr(0, GetSaveLoadErrorString());
-		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 	}
 
 	_settings_game.difficulty = _settings_newgame.difficulty;
@@ -1002,7 +1002,7 @@ void SwitchToMode(SwitchMode new_mode)
 			if (!SafeSaveOrLoad(_file_to_saveload.name, _file_to_saveload.mode, GM_NORMAL, NO_DIRECTORY)) {
 				LoadIntroGame();
 				SetDParamStr(0, GetSaveLoadErrorString());
-				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 			} else {
 				if (_saveload_mode == SLD_LOAD_SCENARIO) {
 					StartupEngines();
@@ -1047,7 +1047,7 @@ void SwitchToMode(SwitchMode new_mode)
 				DoCommandP(0, PM_PAUSED_SAVELOAD, 0, CMD_PAUSE);
 			} else {
 				SetDParamStr(0, GetSaveLoadErrorString());
-				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 			}
 			break;
 		}
@@ -1055,7 +1055,7 @@ void SwitchToMode(SwitchMode new_mode)
 		case SM_MENU: // Switch to game intro menu
 			LoadIntroGame();
 			if (BaseSounds::ini_set == NULL && BaseSounds::GetUsedSet()->fallback) {
-				ShowErrorMessage(STR_WARNING_FALLBACK_SOUNDSET, INVALID_STRING_ID, 0, 0, true);
+				ShowErrorMessage(STR_WARNING_FALLBACK_SOUNDSET, INVALID_STRING_ID, WL_CRITICAL);
 				BaseSounds::ini_set = strdup(BaseSounds::GetUsedSet()->name);
 			}
 			break;
@@ -1064,7 +1064,7 @@ void SwitchToMode(SwitchMode new_mode)
 			/* Make network saved games on pause compatible to singleplayer */
 			if (SaveOrLoad(_file_to_saveload.name, SL_SAVE, NO_DIRECTORY) != SL_OK) {
 				SetDParamStr(0, GetSaveLoadErrorString());
-				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 			} else {
 				DeleteWindowById(WC_SAVELOAD, 0);
 			}
@@ -1081,7 +1081,7 @@ void SwitchToMode(SwitchMode new_mode)
 	}
 
 	if (_switch_mode_errorstr != INVALID_STRING_ID) {
-		ShowErrorMessage(_switch_mode_errorstr, INVALID_STRING_ID, 0, 0, true);
+		ShowErrorMessage(_switch_mode_errorstr, INVALID_STRING_ID, WL_CRITICAL);
 	}
 }
 
@@ -1239,7 +1239,7 @@ static void DoAutosave()
 
 	DEBUG(sl, 2, "Autosaving to '%s'", buf);
 	if (SaveOrLoad(buf, SL_SAVE, AUTOSAVE_DIR) != SL_OK) {
-		ShowErrorMessage(STR_ERROR_AUTOSAVE_FAILED, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_ERROR_AUTOSAVE_FAILED, INVALID_STRING_ID, WL_ERROR);
 	}
 }
 
diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index 0d081df730..7a9c81e98a 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -1743,7 +1743,7 @@ const char *GetSaveLoadErrorString()
 static void SaveFileError()
 {
 	SetDParamStr(0, GetSaveLoadErrorString());
-	ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+	ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 	SaveFileDone();
 }
 
@@ -1833,7 +1833,7 @@ SaveOrLoadResult SaveOrLoad(const char *filename, int mode, Subdirectory sb, boo
 	/* An instance of saving is already active, so don't go saving again */
 	if (_ts.saveinprogress && mode == SL_SAVE) {
 		/* if not an autosave, but a user action, show error message */
-		if (!_do_autosave) ShowErrorMessage(STR_ERROR_SAVE_STILL_IN_PROGRESS, INVALID_STRING_ID, 0, 0);
+		if (!_do_autosave) ShowErrorMessage(STR_ERROR_SAVE_STILL_IN_PROGRESS, INVALID_STRING_ID, WL_ERROR);
 		return SL_OK;
 	}
 	WaitTillSaved();
diff --git a/src/screenshot.cpp b/src/screenshot.cpp
index eb0901fb10..b5198e2764 100644
--- a/src/screenshot.cpp
+++ b/src/screenshot.cpp
@@ -659,9 +659,9 @@ bool MakeScreenshot(ScreenshotType t, const char *name)
 
 	if (ret) {
 		SetDParamStr(0, _screenshot_name);
-		ShowErrorMessage(STR_MESSAGE_SCREENSHOT_SUCCESSFULLY, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_MESSAGE_SCREENSHOT_SUCCESSFULLY, INVALID_STRING_ID, WL_WARNING);
 	} else {
-		ShowErrorMessage(STR_ERROR_SCREENSHOT_FAILED, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_ERROR_SCREENSHOT_FAILED, INVALID_STRING_ID, WL_ERROR);
 	}
 
 	return ret;
diff --git a/src/settings.cpp b/src/settings.cpp
index 9c9dd1f37e..901860848b 100644
--- a/src/settings.cpp
+++ b/src/settings.cpp
@@ -857,7 +857,7 @@ static bool DifficultyChange(int32)
 {
 	if (_game_mode == GM_MENU) {
 		if (_settings_newgame.difficulty.diff_level != 3) {
-			ShowErrorMessage(STR_WARNING_DIFFICULTY_TO_CUSTOM, INVALID_STRING_ID, 0, 0);
+			ShowErrorMessage(STR_WARNING_DIFFICULTY_TO_CUSTOM, INVALID_STRING_ID, WL_WARNING);
 			_settings_newgame.difficulty.diff_level = 3;
 		}
 		SetWindowClassesDirty(WC_SELECT_GAME);
@@ -870,7 +870,7 @@ static bool DifficultyChange(int32)
 			AI::GetInfoList()->size() == 0 &&
 #endif /* ENABLE_AI */
 			(!_networking || _network_server)) {
-		ShowErrorMessage(STR_WARNING_NO_SUITABLE_AI, INVALID_STRING_ID, 0, 0, true);
+		ShowErrorMessage(STR_WARNING_NO_SUITABLE_AI, INVALID_STRING_ID, WL_CRITICAL);
 	}
 
 	/* If we are a network-client, update the difficult setting (if it is open).
@@ -925,14 +925,14 @@ static bool CheckFreeformEdges(int32 p1)
 		Ship *s;
 		FOR_ALL_SHIPS(s) {
 			if (TileX(s->tile) == 0 || TileY(s->tile) == 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_EMPTY, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_EMPTY, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
 		Station *st;
 		FOR_ALL_STATIONS(st) {
 			if (TileX(st->xy) == 0 || TileY(st->xy) == 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_EMPTY, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_EMPTY, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
@@ -941,25 +941,25 @@ static bool CheckFreeformEdges(int32 p1)
 	} else {
 		for (uint i = 0; i < MapMaxX(); i++) {
 			if (TileHeight(TileXY(i, 1)) != 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
 		for (uint i = 1; i < MapMaxX(); i++) {
 			if (!IsTileType(TileXY(i, MapMaxY() - 1), MP_WATER) || TileHeight(TileXY(1, MapMaxY())) != 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
 		for (uint i = 0; i < MapMaxY(); i++) {
 			if (TileHeight(TileXY(1, i)) != 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
 		for (uint i = 1; i < MapMaxY(); i++) {
 			if (!IsTileType(TileXY(MapMaxX() - 1, i), MP_WATER) || TileHeight(TileXY(MapMaxX(), i)) != 0) {
-				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, 0, 0);
+				ShowErrorMessage(STR_CONFIG_SETTING_EDGES_NOT_WATER, INVALID_STRING_ID, WL_ERROR);
 				return false;
 			}
 		}
@@ -988,7 +988,7 @@ static bool ChangeDynamicEngines(int32 p1)
 	const Vehicle *v;
 	FOR_ALL_VEHICLES(v) {
 		if (IsCompanyBuildableVehicleType(v)) {
-			ShowErrorMessage(STR_CONFIG_SETTING_DYNAMIC_ENGINES_EXISTING_VEHICLES, INVALID_STRING_ID, 0, 0);
+			ShowErrorMessage(STR_CONFIG_SETTING_DYNAMIC_ENGINES_EXISTING_VEHICLES, INVALID_STRING_ID, WL_ERROR);
 			return false;
 		}
 	}
diff --git a/src/settings_gui.cpp b/src/settings_gui.cpp
index 0173bfb6d9..70dc8a47c4 100644
--- a/src/settings_gui.cpp
+++ b/src/settings_gui.cpp
@@ -331,7 +331,7 @@ struct GameOptionsWindow : Window {
 			case GOW_FULLSCREEN_BUTTON: // Click fullscreen on/off
 				/* try to toggle full-screen on/off */
 				if (!ToggleFullScreen(!_fullscreen)) {
-					ShowErrorMessage(STR_ERROR_FULLSCREEN_FAILED, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_ERROR_FULLSCREEN_FAILED, INVALID_STRING_ID, WL_ERROR);
 				}
 				this->SetWidgetLoweredState(GOW_FULLSCREEN_BUTTON, _fullscreen);
 				this->SetDirty();
@@ -660,7 +660,7 @@ public:
 					AI::GetInfoList()->size() == 0 &&
 #endif /* ENABLE_AI */
 					this->opt_mod_temp.difficulty.max_no_competitors != 0) {
-				ShowErrorMessage(STR_WARNING_NO_SUITABLE_AI, INVALID_STRING_ID, 0, 0, true);
+				ShowErrorMessage(STR_WARNING_NO_SUITABLE_AI, INVALID_STRING_ID, WL_CRITICAL);
 			}
 			return;
 		}
diff --git a/src/spriteloader/grf.cpp b/src/spriteloader/grf.cpp
index de47201e16..335daa1a2d 100644
--- a/src/spriteloader/grf.cpp
+++ b/src/spriteloader/grf.cpp
@@ -31,7 +31,7 @@ static bool WarnCorruptSprite(uint8 file_slot, size_t file_pos, int line)
 	static byte warning_level = 0;
 	if (warning_level == 0) {
 		SetDParamStr(0, FioGetFilename(file_slot));
-		ShowErrorMessage(STR_NEWGRF_ERROR_CORRUPT_SPRITE, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_NEWGRF_ERROR_CORRUPT_SPRITE, INVALID_STRING_ID, WL_ERROR);
 	}
 	DEBUG(sprite, warning_level, "[%i] Loading corrupted sprite from %s at position %i", line, FioGetFilename(file_slot), (int)file_pos);
 	warning_level = 6;
diff --git a/src/strings.cpp b/src/strings.cpp
index e27560b53f..11c8c587fe 100644
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -1602,7 +1602,7 @@ void CheckForMissingGlyphsInLoadedLanguagePack()
 						static char *err_str = strdup("XXXThe current font is missing some of the characters used in the texts for this language. Read the readme to see how to solve this.");
 						Utf8Encode(err_str, SCC_YELLOW);
 						SetDParamStr(0, err_str);
-						ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+						ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_WARNING);
 
 						/* Reset the font width */
 						LoadStringWidthTable();
@@ -1635,7 +1635,7 @@ void CheckForMissingGlyphsInLoadedLanguagePack()
 		static char *err_str = strdup("XXXThis version of OpenTTD does not support right-to-left languages. Recompile with icu enabled.");
 		Utf8Encode(err_str, SCC_YELLOW);
 		SetDParamStr(0, err_str);
-		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_JUST_RAW_STRING, INVALID_STRING_ID, WL_ERROR);
 	}
 #endif
 }
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index 6ab50c3ff9..637405a657 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -2309,7 +2309,7 @@ void ExpandTown(Town *t)
 	 * but do this only onces per openttd run. */
 	static bool warned_no_roads = false;
 	if (!_settings_game.economy.allow_town_roads && !warned_no_roads) {
-		ShowErrorMessage(STR_ERROR_TOWN_EXPAND_WARN_NO_ROADS, INVALID_STRING_ID, 0, 0);
+		ShowErrorMessage(STR_ERROR_TOWN_EXPAND_WARN_NO_ROADS, INVALID_STRING_ID, WL_WARNING);
 		warned_no_roads = true;
 	}
 
@@ -2453,7 +2453,7 @@ static void TownActionBribe(Town *t)
 
 		/* only show errormessage to the executing player. All errors are handled command.c
 		 * but this is special, because it can only 'fail' on a DC_EXEC */
-		if (IsLocalCompany()) ShowErrorMessage(STR_ERROR_BRIBE_FAILED, STR_ERROR_BRIBE_FAILED_2, 0, 0);
+		if (IsLocalCompany()) ShowErrorMessage(STR_ERROR_BRIBE_FAILED, STR_ERROR_BRIBE_FAILED_2, WL_INFO);
 
 		/* decrease by a lot!
 		 * ChangeTownRating is only for stuff in demolishing. Bribe failure should
diff --git a/src/town_gui.cpp b/src/town_gui.cpp
index 56732d5d83..c479939bf5 100644
--- a/src/town_gui.cpp
+++ b/src/town_gui.cpp
@@ -462,7 +462,7 @@ public:
 				if (this->CanDeleteTown()) {
 					delete this->town;
 				} else {
-					ShowErrorMessage(STR_ERROR_TOWN_CAN_T_DELETE, INVALID_STRING_ID, 0, 0);
+					ShowErrorMessage(STR_ERROR_TOWN_CAN_T_DELETE, INVALID_STRING_ID, WL_INFO);
 				}
 				break;
 		}
@@ -1149,7 +1149,7 @@ public:
 				_generating_world = true;
 				UpdateNearestTownForRoadTiles(true);
 				if (!GenerateTowns(this->town_layout)) {
-					ShowErrorMessage(STR_ERROR_CAN_T_GENERATE_TOWN, STR_ERROR_NO_SPACE_FOR_TOWN, 0, 0);
+					ShowErrorMessage(STR_ERROR_CAN_T_GENERATE_TOWN, STR_ERROR_NO_SPACE_FOR_TOWN, WL_INFO);
 				}
 				UpdateNearestTownForRoadTiles(false);
 				_generating_world = false;
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index 0f2ae36b22..976fe6467c 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -186,7 +186,7 @@ void CheckTrainsLengths()
 							(w->track == TRACK_BIT_DEPOT && TicksToLeaveDepot(u) <= 0)) {
 						SetDParam(0, v->index);
 						SetDParam(1, v->owner);
-						ShowErrorMessage(STR_BROKEN_VEHICLE_LENGTH, INVALID_STRING_ID, 0, 0, true);
+						ShowErrorMessage(STR_BROKEN_VEHICLE_LENGTH, INVALID_STRING_ID, WL_CRITICAL);
 
 						if (!_networking) DoCommandP(0, PM_PAUSED_ERROR, 1, CMD_PAUSE);
 					}
diff --git a/src/vehicle.cpp b/src/vehicle.cpp
index f0a1d40daf..a8968db8d9 100644
--- a/src/vehicle.cpp
+++ b/src/vehicle.cpp
@@ -202,7 +202,7 @@ void ShowNewGrfVehicleError(EngineID engine, StringID part1, StringID part2, GRF
 		SetBit(grfconfig->grf_bugs, bug_type);
 		SetDParamStr(0, grfconfig->name);
 		SetDParam(1, engine);
-		ShowErrorMessage(part1, part2, 0, 0, true);
+		ShowErrorMessage(part1, part2, WL_CRITICAL);
 		if (!_networking) DoCommand(0, critical ? PM_PAUSED_ERROR : PM_PAUSED_NORMAL, 1, DC_EXEC, CMD_PAUSE);
 	}