For the Steam version, did you try verifying local files? In the Steam library, right click on Divinity Original Sin and select Properties, switch to the Local Files tab and then click on the 'Verify Integrity of Game Cache...' button.
Try browsing to the '..\Documents\Larian Studios' folder and renaming the 'Divinity Original Sin' subfolder.
This folder contains the saved games, configuration files and a level cache folder. Deleting or renaming it will get the game to recreate it on startup; playing the game from a different Windows user account would effectively do the same thing.
After that, start D:OS and see if you get the same error. If not, create a new profile, exit and then move/copy your saves from the renamed folder into the newly created profile's savegames folder.
If you still get the error, exit, delete the new My Documents D:OS folder and rename the original back again.
