I've just recently traded up from a 20gb XBox 360 Pro to a pre-owned 120gb XBox 360 Elite which had a reformatted hard drive in it; nothing of use on the drive. I've recovered my Gamertag and redownloaded all my purchases etc using my download history. Of course; no Hexic HD. Luckily I gave my old 360 to my kid sister. Anyway, I've tried copying the game over using both a usb thumb drive and a 256mb XBox 360 memory unit to no avail. It wouldn't even recognise the usb stick as a valid destination and kept on saying that copying it to the memory unit was not allowed.
Anyway, I've spoken to Support and mentioned the code but instead of providing a code or anything the lady spoke to her supervisor and then suggested I send away to MS UK for a Data Migration Kit. Will await the arrival of that and see if that works. If not, I guess I'll be back on the phone to Support again.