So I just put my EF-S 17-85mm lens onto my 40d, and got an error message saying "Err 01 Communications between the camera and lens if faulty. Clean the lens contacts." The contacts are clean. It only does this when the focal length is in the range of 17 to 24mm, greater than 24mm and it works fine. I can still use it in the 17-24mm range but only at the minimum aperture of f/4. What would cause this? I'm picking it may be a fault with a ribbon cable inside but really don't know. The lens is not under any sort of warranty, and I bought it second hand. What should I do?