Anybody else have this problem!!! Found how to fix it for most people!
1. Go to the Xbox 360 menu and click on "Memory"
2. When there, press: X X LB RB XX
3. A message will pop up asking if you want to perform maintenance on your 360, so click yes.
This will clear your cache, and the game will work fine after that. Also, don't worry, as none of your saved games will be erased.