I first looked for advice online. People have had similar issues, and it apparently hasn't been fixed by any sort of patch, at least not for Xbox 360. I also discovered several possible "fixes" : ranging from completing some other quests and coming back, to clearing the game cache, but neither yielded results.
So, not wanting to give up my awesome character, I decided I'd continue on doing other quests, with the hopeful deduction that this might help squash the bug. I proceeded over the next month doing every single other quest in the game. Alas, I am now staring once again at an uncooperative loading screen.
Is there any other piece of advice anyone can give me? It's really disheartening to see a file with over 126 hours put into it not be able to complete the main questline.
Thanks