Thanks for the note!
It's a very strange bug... I had it myself too, only in my case it was an invisible enemy army.And if you attack it, you get a CTD. Have you maybe tried to attack something with your invisible army?Second, I fiddled with the invisible army crash. It continued into the next turn when I tried to take all my troops out of the minor city. But when I took each unit out one at a time, I had no invisible army issue. Onto Roma!