I have the same issue and discovered it in the exact same manor.
Save/Load seemed to work better after I found the larian folder in my documents folder and ensured no read only files existed in the folder or subfolders however it did not completely fix the problem. When attempting to play more Autosave became an issue on the second autosave in the dungeon. After that I gave up concluding this game is unplayable until this is fixed.
Quite frankly its pretty embarrassing that the save/load code is not better guarded. This is one of the most basic features in a game and its beyond me why this isn't rock solid.
I'm running Win 7 32 bit on a Lenovo W510 laptop. I however (contrary to the above poster) have kasperski antivirus running and do not have the option to turn it off.
Edit Update- It looks like I managed to fix the issue by following this advice:
Create a shortcut with administrator privileges
In Steam go to Library, right click Divinity original Sin -> Properties -> Local Files -> Browse Local Files -> Go to "Shipping" -> Right Click EoCApp.exe and create a desktop shortcut.
Then right click the new shortcut -> properties -> Compatibility -> TICK "Run this program as an administrator".
Run the game from this shortcut instead of the one steam created for you.
