Try starting the game directly from the '..\SteamApps\common\Divinity - Original Sin\Shipping\EoCApp.exe' program file, by right clicking and running as administrator. Create a new profile, start a game quickly, save, exit and restart the game, and see if running as administrator will get it to read the profile.
It shouldn't matter is the game is installed on another drive, the profiles, etc, should be in the 'My Documents\Larian Studios\Divinity Original Sin' folder, which is generally on the c: drive by default.
