Every other shoot or so my lens stops autofocusing on my D300s. This has been happening for some time now. The other week or so I noticed that I somehow nudged the Focus Mode Selector into M. "Aha!" I exclaimed. "I'll never do that again!". Sigh, I did it twice last yesterday. I really can't figure out how I'm doing this. I'm fairly certain it is NOT when I'm actually shooting. It's gotta be when I'm swinging my camera up to my eye or when I'm chimping. This is making me craaaaaazy! Cheers, Dave
"Stupidity is a gift from God, but one mustn't misuse it" - Pope John Paul II
First, Take a deep breath and relax! Not that it matters much but; Is it the mode selector on the camera body or the switch on the lens?
If it was not happening before: Are you using a new bag or strap? Does the switch feel loose?
If none of the above, you must be inadvertantly touching the switch when you pick up the camera. Pay attention to how you are picking it up or holding it and you should be able to prevent it from happening again.
I developed that problem with my D300. I eventually figured out that I was doing it in the heat of the moment when shifting to the portrait position. I don't have a grip so my left hand is supporting my camera right next to the switch.
When I first got my D200 I found that I would periodically bump the focus selector switch on the camera body. When I did a bit of research on the web I found that many others had the same problem. As far as I know the only solution that anybody ever came up with is to be more aware and more careful when picking up and handling the camera.
If the switch you are having trouble with is the one on the lens, you may be able to cover it with a piece of tape. ...but I have never heard a definitive solution for hitting the switch on the body.