Well... maybe deleting the profiles from the Documents folder and running the game as an administrator could help.
I've never encountered this bug, but once I fixed a bug by changing the profile. For some reason, it was corrupting the saves. Maybe something similar is happening now.
It's extremely frustrating if I have to delete the installed creatures... A lot of work was put into it.
UPD1. I figured it out. Here it is. I went through a bunch of files - here they are, the buggy culprits. They are causing the problems. Specifically, the NCF_Skelen1 file. It's strange that because of just one creature, the game won't even launch without an error, like "CREATURE 999 has no visual."
UPD2. I'm glad I solved the launch problem. I don't understand what I did wrong with these creatures. I was modifying them using castle IDs. It's all my fault, I guess. I'm just not very good at this yet. I can't seem to transfer them from castle IDs yet