Bad picks and the fumble. Oh, and not throwing to wide open guys to keep the play running; I think that Allen is great, don't get me wrong, but sometimes you have to take what the game gives you. Doing so doesn't make him Trent Edwards, not by a long shot.
Lots of other blame to go around. Giving up 3rd and longs on defense, questionable play calling on O, not taking the FG, and so on.