I was getting this error as well when I first tried it out. Keep in mind, I went directly to the music store export section before redeeming my code to get my download code. After taking a better look at the instructions, I went on my pc, and recieved my token code. Went back onto Xbox, hit the redeem code section and got the export key. From there, I went back to the game menu export section and all worked perfectly.
Now, I don't know if it was just coincidence that the error didn't come up once I followed the proper steps or not but from what I'm seeing above, most people are doing all the steps correctly and still getting it.
I'm sure it has nothing to do with the disc itself. Could be a corrupt file of dlc on the hard drive I suppose, but the error just corrected itself for me. Maybe clearing the cache on the hard drive may help??
Just thought I would throw my version of what happened to see if it helps answer anyones problems, questions or concearns. Aside from that, you just wasted your time reading this.