I just upgraded to a full frame body (D600) and cannot get my 50mm 1.8D lens to connect. The only time the camera connects with the lens is when it's set to auto and the lens is locked at F/4, but the focus is very slow (it seems like the camera is struggling). When I switch the body into manual mode, the FEE error is constant-- even when I lock the lens at F/22. Any ideas as to what's going on and how I can fix it? Thanks!