The only chance you have of fixing it is to delete Knights of the Nine from your xbox, complete the quest, then re-download it (you can do this for free if you bought it). You'll loose all progress in the KotN expansion though and will have to start it again. Also any items in any KotN areas will be deleted.
That's the best solution yet. I was nervous about deleting the KotN and then having it still not work, but i'll try that and update this thread appropriately. Thank you.