This happened to my recent campaign save - it's doomed! I think this kind of thing just happens occasionally and I don't know if there's a solution other than to revert to an earlier save and hope the problem doesn't reoccur later. I tend to use 3-4 saves for my campaigns, saving every hour or so in one of the save locations. However, sometimes I rely on Quicksave a bit too much. Fortunately for me, my previous save before the corruption/problem was just an hour beforehand, so hopefully I haven't lost much (although I suspect the great victory over the scottish rebels where I slaughtered 1800 men for the loss of about 25 men has gone).

So basically, if all else fails, go back to an earlier save and fingers crossed, you'll be ok from then on. It sucks, but what can we mere peasants do.