I have 46 cities, but for some reason I can no longer attack cities, nor can I raze any of my current cities. Each time I try to finish off the city, it just goes to the next unit. The same happens if I try to attack with that unit. I can nuke, bomb and shoot it to the last HP, but I can't "enter" the city.
I'm currently using Modern Tank, Mechanized Infantry, Artillery and Paratroopers. It wasn't a problem before. I conquered a lot of cities using Tanks.
Is there a limit on cities, or could something else be causing this?