Hello,
Firstly, I'd like to point out that this is a duplicate of three bug reports (here (https://forum.simutrans.com/index.php?topic=21306.0), also here (https://forum.simutrans.com/index.php?topic=21907.0), and on Steam (https://steamcommunity.com/app/434520/discussions/10/803471225741608860/)), which I was unable to respond to. However, I think I have found a way to reliably reproduce the bug, as I have managed to do so on two different Windows machines using the Steam version. The bug occurs when you try to start Simutrans-Ex, on the pak selector UI, after playing with themes and shutting down the game for the first time.
The error prompt is:
https://1drv.ms/i/c/24b12fc3d94e8d3c/IQCgoIz5VfC2QKMtPQucsjrtAQqcCD5RQA20WfPyDdEPFGY
FATAL ERROR: gui_theme_t :: init_gui_themes - Wrong theme loaded
Aborting program execution ...
This is done by doing the following:
- Set the theme to Simutrans New, Simutrans Classic (the size doesn't matter), or pak64.german.
- Set the theme to another theme that does not update all its components properly. For instance, purple night or silver.
- Quit the game.
- Relaunch.
Note that the broken theme should look like this (in the case you select Simutrans Classic then Purple Night):
https://1drv.ms/i/c/24b12fc3d94e8d3c/IQAAIZfj1xbnQ4p4qf9ZjnYTAUjGCu1VVjQQFtzJAuNtYpU
I have not tested with all theme combinations, and always made the theme changes on britain-ex pak. I have tested it with pak64.german (at step 1) and Silver (at step 2) and encountered the same error. In this case, Silver just looks like pak64.german but with a silver color (instead of... well idk what it's supposed to look like lol), as seen here:
https://1drv.ms/i/c/24b12fc3d94e8d3c/IQBgx3BULrMORqugCkyTkHJ7Ae7bQV7d4eIuJsbhYLry5z4
It seems that, since those themes do not update all components, and that the theme is needed for the pak selector, the game breaks.
A simple fix is to simply delete the settings-extended.xml file from ~\Documents\Simutrans. It resets the theme.
PS: Tried to upload the images using the forum's file uploader. It did not work.
Since it's unrelated to this bug, I'll simply add it here: I've found that the 'label style' (found in display settings) is not saved either. While this is a minor bug that will probably not be fixed, I absolutely hate the default setting.