Another potential problem of the non "C" lenses that I have read about. The older lens diapragm may cause a problem with the pro s and sd as, it was related by the photographer, these lens diapragms are stiffer than the s and sd's causing stress on the lens mechanics and possible premature failure.
I have a 65mm non "C" and have had no probs in the year I have used it. I merely had to attach a spacer ring (friction fit) and voila. Works fine. (The spacer ring is required to stop potential light leaks on the SD.