I think I finally found the fix
Hi,
Like all of you I have been trying with no success to export the songs from Lego RB and getting that Error Code 800.. (even after downloading the Lego Rock Band Export Pack (that has the license key), well I finally got it to work.
I tried the steps people have put down and nothing seemed to work, called Xbox support and after being on the phone with them for more than an hour zip. Well here is what worked for me. YMMV
(Note: I have changed my Xbox more than once and still have same HD, this may have been what was causing the issue for me)
Also please be aware that this may not be the solution for everyone, but after many different tries this is what finally worked for me.
1. Get the code for Lego Rock Band and enter it in Redeem code and download license key (Lego Rock Band Export Pack) 108k
2. Go to Memory/HD/Games/Rock Band/ Rock Band Export License (Original Rock Band, NOT EVERYONE WILL HAVE IT, BUT THIS SEEMED TO MAKE THE DIFFERENCE FOR ME) Delete it.
3. Go to Memory/HD/Games/Rock Band/Lego Rock Band Export Pack and delete it.
4. Go to Memory/HD/System Files/Delete Xbox Marketplace Data and Rights DB.
5. Go back to Memory and right before you enter the Hard Drive hit Y and select Delete System Cache.
6. Back out and Power off your Xbox 360 and wait about 30 seconds to turn it back on.
7. Power Xbox 360 back on and make sure you are logged onto Xbox Live.
8. On the Tab where it shows your Avatar go to My Account/Purchase History.
9. Scroll Down until you find Rock Band Export License and redownload it.
10. NOW Launch Lego Rock Band Game (Free Play and make sure that I could see and play Rock Band 1 songs which might have reauthorized the console, I could)
11. Go out to the Dashboard and Redownload the Lego Rock Band Export Pack from Purchase History
12. Launch Lego Rock Band, got to the Store and go down to Export and you should now be able to Purchase the pack. (Make sure you have the 800 Points of course)
Seems Long and convoluted but I wasn't able to do anything since Tuesday and after many tries this is what worked for me, hope it helps you too.
Good Luck