Originally Posted by
DimeBagHo
I think I know what caused the problem. That kind of error, with messed up region owners, is usually caused by map changes. Even very slight changes to the shape of one region can change the internal region ids for large parts of the map. In the last couple of versions I fixed some problems with the land bridges. That hasn't caused this sort of problem in the past, but this time it must have made a difference to a region shape and broken saved-game compatibility.
BTW, switching exes will also cause problems, but it usually looks a bit different. Instead of region owners being messed up, you will lose the background map in the mini-map.