I am having the same problem. I just wanted to load a level to generate a character portrait.
Any ideas on what to do? Tiqon's advice is a bit baffling to me (not his fault, all mine). What properties am I looking at where?
In Steam, you can right click the game and choose properties. In that screen you have an option to verify the local file integrety (its on the second pane I think, I'm at work so can't check and my old feebleed mind is not sure :D).
But I realize that maybe you have the game from GOG?
Anyways, it should not BE so you have to do this, it just worked for me a couple of time. Could have been a coincident
I hope you all get it to work.