Turn all graphic settings on low, including anti-aliasing.
It's a common error late game when the computer runs out of RAM or graphics memory. Setting settings on low will give your more memory to run with.
(FYI, I always play on low settings. Faster turns & better games).
Thanks! I have done so and the game has only freezed one time. How do you turn off anti-aliasing? I did not see that anywhere.