HELP!!! I have a 9mm Shield that I've run about 500 rounds through. I have field stripped it several times with no problems. Now, however, I can't get the slide off. It stops about 1/4 inch past where it normally sits when ready to fire. It is coming up against something solid. I've tried both methods of field stripping (activating sear lever and not, but pulling trigger instead). Nothing works. Can anyone help me out?