It was Esbern not coming out of his room in the Ratway Sewers when he was supposed to. I'm really fuzzy on the details now, but from what I remember there are multiple bugs related to him. Some have been patched, either officially or community, but the one I hit hadn't been.
OH! I hit that one too, quit the game over it. Very obnoxious finding endless forum posts of people having the same bug as you, and not a solution to be had, and your not even being paid for it.
