I am trying to sell my Nikon 55-200mm AF-S VR lens. I met up with the buyer this morning. He mounted my lens on his D40 body and said the AF doesn't work. I tried it on his camera, indeed it didn't work. Check his settings, all look good(not familiar with the D40 though). Took the lens off and mounted it on my D5000, and AF worked. I noticed the inside of his body was quite dusty. Could that have caused it? He also said his 18-55mm autofocuses. I am kind of puzzled. What could it have been?