Errors 304 and 116 are both problems loading the story.
If you create a new profile and start a new game, can you save and reload?
If a new game works, the issues is probably something in the save itself. If you zip your latest save and email it to supportdos@larian.com, I can check it out here. In earlier patches there were changes to the file format and checks added to the load process to try to avoid or detect and fix (where possible) the common types of situations that could result in corrupt information. Unfortunately, at this point, if something becomes corrupt in a save, it is most likely not fixable.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin\PlayerProfiles\<ProfileName>\Savegames' folder. In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipper) Folder'.
You can increase the number of quicksaves and autosaves kept in the Game options, which will reduce the chance of overwriting a working save if something happens to corrupt a new save.
Periodic named saves also provide a more reliable method to get back to a previous working state, if you do run into a problem (or just want to try a quest a different way, or change a character build choice, etc).