OK, so I have a BG-E2N grip going on a 50D. The black knob/wheel that turns the screw for the mounting screw only turns so far then stops. What this causes it the grip won't screw all the way into the tripod mount. Nothing is stripped on either piece. It's the black wheel on the grip that is the problem. Should it freely spin continuously or does it stop after about 3/4 of a turn like mine does? The camera mounts to a tripod just fine so I know the camera mount is ok.