Can you start a new game, save (under a new name) and load that saved game?
If a new save works, the problem is likely in the other saves; if neither work the problem may be the game itself, in which case re-installing the game may help.
Try deleting all of the files in the '..\Divine Divinity\Run\Dynamic' folder ('..\Divine Divinity\Dynamic' in the download version).
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 folder (in '..\Divine Divinity\Run\savegames' in the disk version, or '..\Divine Divinity\savegames' for the download version).
Under Vista/7, depending on how the user accounts are set up, if you install the game to the default Program Files path, Windows can create separate savegame folders for each user, and then map that folder to the game's savegame folder (so it will just see the saves for the relevant user).
C:\Users\ %account name% \AppData\Local\VirtualStore\Program Files\Divine Divinity\[Run\]savegames
Missing files might cause the game to crash when trying to load. After getting to the wastelands each save folder should have 37 files, and once you enter the Black Ring dungeon it should have 42.
If the saved game folders have .tmp extensions, it means there was a problem during the save process and it didn't complete properly.
One person had a crash in Windows 5 or 10 minutes after exiting the game, and on rebooting Windows decided there was a problem with the (zero byte) inv.b2 file in all the recent saves, and deleted them. Fortunately this file can easily be replaced.
Are you shutting down all non-essential programs (especially anti-virus) before starting the game?
