Since the betas, I have never been unable to cast a spell within a city. For instance, if summoning a creature, I always have to cast the spell beyond the city itself.
This was not a huge problem; however, I recently tried to cast a spell to improve city performance--hadn't tried that before--and, once again, the spell could not be cast. This is more of a problem than not being able to summon creatures within the city!
Is there something simple I'm missing?