Today my Simutrans world stopped working for the same reason.
I had two saves and neither of them worked,
It's strange because last time I only save file named "3"
Linux, intel 64 bit, ubuntu 24.
YOu need to be a little more specific on what stopped to work. Maybe rather make a new topic in help for this.
I've split this and put it in the right place.
Welcome Krzysztof — please do reply with more details about any errors, what pakset you're using, anything else that might help reproduce please.