Did you notice this in the readme text file?
Problem: Black squares appear around the imagery in the game
Cause: Your video card does not support color keying.
Solution: Turn on the alpha bit in the configuration tool.
I don't know if that could cause a problem with some images but not others, though.
Try deleting all of the files in the '
..\Divine Divinity\Run\Dynamic' folder.
This folder is used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied from that folder when you save a game. The files will be re-created as required the next time you start Divinity. If there was a corrupt file in that folder, deleting the files should fix the problem.