Hi David,
Cleaning the contacts on the rear of the lens was a good idea. Often that can help. Not sure how you cleaned it, I recommend carefully wiping them with a clean, lint free rag slightly dampened with a few drops of isopropyl (rubbing) alcohol. Keep off the lens optics, of course.
Also check that the corresponding pins just inside the front of the camera are okay. Those are spring loaded and if you put slight pressure on them should give a little, then spring back into place. On rare occasion one or more of those might get stuck and no longer make good contact.
Operate the switches on the lens a dozen or two dozen times, and see if that helps. Most switches are self-cleaning. If left in one position for a long time, oxidization might gradually build up in them and eventually cause connectivity problems. But simply using them a few times this often will clear up and they'll work again.
Otherwise, it's possibly a failed ribbon cable or connector inside the lens, which will mean a trip to the service dept. for repair. It also could be a fault of some sort in the camera, though I think from your description that's less likely. If you could test the lens on another camera, and the camera with a different lens, you might be able to narrow it down to one or the other.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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