Where did you purchase the hard drive that's currently in your console from? If you purchased this hard drive separately from a 3rd party website such as eBay or Amazon Marketplace you might not have yourself a genuine hard drive.
Only genuine Xbox 360 hard drives manufactured by Microsoft have the emulation files needed to play original Xbox titles. If you have a 3rd party hard drive you'll more than likely get an error suggesting that you re-download the content even if it was a disc
based original game. I'd suggest checking that first.
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