Hmmm now this is interesting... I loaded up the autosave as you suggested and bam, the next turn I had the error pop up when it came to the eleutheroi's turn. I then again loaded up the same autosave, doing exactly the same things, made a manual save and then clicked end turn. Lo and behold, I made it to the next turn!

Just as I was feeling happy about this good fortune when the error creeped up again the next turn later on the eleutheroi's turn.