Try browsing to the '..\Documents\Larian Studios' folder and renaming the 'Divinity Original Sin' subfolder. After that try starting a new game and see if you can save. This folder contains the profiles, 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 (don't know about Mac).
Renaming the above mentioned folder worked wonders for me. I have not crashed when saving/zoning since. Thanks.