I'm not sure how to get the game to save properly on your system, but I'll try literally helping you save your game. Email me (raze@larian.com) a save (or post/PM a download link) before entering the Black Cove (or before finding the star stone), and I'll try it and see if I can save. Even if it works here, you may still get a crash either loading or re-saving there, but it's worth a shot.
I will not be up much longer tonight, though...
The save folders are in the '..\Documents\Larian Studios\Divinity Original Sin\Savegames' folder. In Windows Explorer right click a folder and select 'Send To | Compressed Folder' to zip it.
