SimCity - Can't add second city in a region

I have SimCity for Mac--just downloaded in the last week. When I start a new region, there is no problem. I can play the first city in the region, and save/come/go as I please. However, when I go to add a second city, the game loops on the "Now Entering..." screen. The game tips scroll across the bottom, but the city never loads. When I'm on this screen, the city name does not display (normally it is in large blue letters in the middle of the screen). I have to force quit the program to get off of this screen.

This problem has repeated itself in every region I try. I can basically have one city in every region, but no more. I spoke with a game advisor on the phone yesterday, and he suggested uninstalling and reinstalling. I've tried this a couple times, and the problem persists.

Note, I am playing single-player in sandbox mode, if that makes a difference.

Also, I previously downloaded the game through my Origin account on a PC. We then decided to buy a Mac, so I uninstalled the game on the PC and have been running it on the Mac. I didn't get to the point of adding a second city to a region on the PC, so I'm not sure if I would have had the same issue there.