I just called in on this issue, My xbox was doing this, first i tried deleting the data (the game and the add on had been loaded to the hard drive) also I tried moving the last save off the hard drive, none of these corrected the issue for me.
What appears to have corrected it was I recoverd the game tag and it let me apply a new update.
If this doesnt work for you then the problem is on the server end.
Side notes: All my other titles had no issue, red dead redemption and the add ons worked when gta4 wouldnt. Also I recently had to have a manual transfer of my profile to a new xbox slim, which may have inspired this issue.