My xbox game won't play on xbox 360, Help?

Well i just updated my Xbox 360 to the latest version, and my Xbox has a hard drive so my original Xbox game won't play. It's Buffy The Vampire Slayer: Chaos Bleeds, its a compatible disk, and it wont work it says if i get an update blah blah blah, but i did and i'm sure of it. It's getting me frustrated because i really want to play that game-.- Plzzzzzzzzzzzzzzz any help would be great i'm desperate, Thanks Though^.^