how did you manage to use the same key over and over again? i have a downloaded copy of the game. i opened up a second account on my pc - started the game. it asked for a serial - i put in the one the game came with and voila the game started. then it asked me to log in to a gamertag which i then created on xbox.com. but: then it asked me again for a serial but mine is wrong... any idea what i could do? thanks!