It could be because you are using backups. Maybe try using real FORZA disc and then see the results. I wish you good luck.
This didn't work. I have two original xboxes and an Xbox 360. I loaded Forza into the 360, and loaded the other boxes with backups on their respective hard drives. I tried to use the multi-screen function to make the game interesting. When the race is about to start, right at the end of the countdown, the game freezes. It doesn't come back. Any thoughts?