This may not help, since only some saves are affected, but 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.
Check the number of files in the saved game folders which do not load (in '
..\Divine Divinity\Run\savegames'). Missing files might cause the game to crash. A new game should have 22 files, after going to either Verdistis or the Dark Forest it should have 27 and after going to both it should have 32.
Troubleshooting Tips (& manual install procedure) 
