My nikkor 85mm f/1.8 D seems to be messed up.. it was working fine when all of a sudden the displayon my nikon d-50 shows "F--" .. its unable to autofocus, can't set the f-stop.. etc. I can manually focus but i can't set the aperture.. Its happened before and i gave it a 'whack' once.. and it was ok. That treatment doesn't seem to be working right now! Is this a significant problem? Or is it one that nikon service should be able to fix pretty easily? I don't want to spend too much time or money.. i'd rather just buy a new lens but i'm concerned it might happen again. All my other lenses work fine.