Unable To Load Game Error

Hi All
A common error that I keep encountering is that saved games will sometimes fail to load. Saving a game each turn and switching on Autosave has helped but the problem does keep recurring. Normally I just ignore the error and go back to the last saved game and it usually works but in the case of today I went to load the game and the last 4 saved games (including autosaves) all fail to load.

I don't really want to repeat the 3 hours of play again! Does anyone have any suggestions? Is this a common problem? I searched the forum and couldn't find the same problem solved.
I've tried restarting the game and done a full reinstall but no change.
I'm playing on 1.35 with Unnamed's Stock AI Mod.
Any suggestions welcome.