Not sure where to go on this issue. After about 3 hours of shooting I get an Error 99 on my camera. I have the problem traced down to this lens. I only get this error when I try to use this lens. I cleaned the contacts on the lens and I still get the error. First, are there anything else I can check on this lens to fix the problems and two, is it worth to take in to get repaired? Any help would be great, thanks.