Nikon 20-35 f/2.8 AFD doesn't want to autofocus all of the time

I have a Nikon 20-35 f/2.8 AFD lens that I'm having problems with.

When it is set to "A" ( and the camera is set to "S") it very often

doesn't want to focus. I'm not saying it can't find a focus point to

focus on, I'm saying that it doesn't even want to try to focus. If I

put the lens to "M" and futz with the focus ring and then put it back

to "A" it sometimes will work, or not. Any ideas on what would cause

this sort of a problem? This happens when it is on my F100 and my

D100, so it's not a body related problem.

 

Thanks in advance.

Dirty contacts? A lot of 'lens communication' problems with Nikon seem to trace back to the contacts between lens and body. If you're in a hurry, sometimes a dismount / mount of the lens will get it going again, but it might be worth having a close look at the contacts and giving them a bit of cleaning.