[Loren]

It means there is no space left on the battleground. I've been trying to get them to listen for some versions now and gotten nowhere. I have posted multiple examples of turn files that will go boom, nothing has ever come of it.

If you examine a debug log of the turn generation you can figure out what province is causing it and reduce the forces there or eliminate the battle entirely in most cases.

There was an old bug where it happened in fortress battles that they fixed, every one I've traced since has turned out to simply be large armies, especially of larger creatures that don't pack multiple creatures per square.