A city that doesn't exist.

I made it to the last scenario of the "The Price of Loyalty" campaign, and I was almost victorious, but one of the enemy cities turned out to be bugged. It is displayed visually, and information about it appears when you right-click on it (including information about the enemy army in the garrison), but the cursor doesn't allow me to enter the city through the gates, and the hero enters the city as if it were empty. Is there a way to capture this "city that doesn't exist" without cheating?