I had the same problem. I couldn't get it off of a 15-91. I got frustrated and left it and went to work. When I came home my wonderful DH managed to get it off. I guess I forgot to turn a light off in the room and when he went in he saw what I was trying to do. (saw the manual out and such) He managed to get it off. I'm not sure how other than he is a lot stronger than I am. I asked him if I had missed a screw or something. He said no it was just really stuck on.