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You can change the title… but i did it for you. also put it in a category for you 
I have no idea what could cause this.
@PatrickKlug, @Mafalda
Hi there and sorry about this trouble!
This error message most likely connected with a corrupted save file. Can you perhaps try to verify your Steam cache, and load up a new game?
Before the error message appears, press ESC and start up a new game file. After doing this, overwrite your previous save file and the error message shouldn’t appear again.
Hope this helps!
Errors like this can happen if you’ve disabled a mod that was previously enabled. Unfortunately, once a save is corrupted, there is not much you can do but start a new one. 