I started a GC and played 21 turns without a problem then on my 22nd turn the game crashes after I end my turn and it cycles all the other nations. I dont think it is a system problem, but here are my specs just in case...

Q6600 (2.4 ghz x4)
8800GTS 640mb
8G DDR2
Vista 64

I'm not sure what the issue is. I tried an earlier save and got the same thing on the same turn. Any ideas?