Just spent 30 minutes on the phone with XBL customer service, and no help was found. They tried vigilantly but I can't get it to work. I entered my code from my case at Harmonix's site and I got the code for my email. I entered the code on xbox.com's account management page via my PC. I was able to DL the LEGO Rock Band Export Key, but when I go to the Music Store and try to download the Export file, I get:
"Can't retrieve information from Xbox LIVE. Please try again later. Status Code: 800700e8"
I cleared my cache, deleted the file, redownloaded it, and I still can't get the export pack to download! Frustrating.