I have this F-- error on my Nikon D50. I have been to several forums, where I have discovered that it's a problem of communication between the lens and camera body. I have cleaned the contacts on both sides - camera and lens - on several occasions, but unfortunately, this error has gone from intermittent to now being permanent.
I have been in contact with Nikon USA, who have advised me that service is required, and I should send the camera in. I'd like to know if anyone else has encountered this problem, and solved it without sending it away to Nikon. Unfortunately, sending it in will be a little difficult, as I'm located in Nigeria.
If it is a Non-G lens - G lenses do NOT have a manual aperture ring - then the aperture ring must be sent to the smallest aperture. Nikon lenses with an aperture ring have a small sliding lock that will prevent the ring from moving from the smallest aperture (typically f/22).
G lenses will not have this problem (as there is no ring to lock; it is already set to its smallest aperture).
Let us know what lens you have? Does it only happen with one lens? Have you tried other lenses?
I think if you get the same error with either lens attached then the decision to send the camera body in for repair is a good one. The error could be coming from a lens but to have two defective lenses at about the same time would not be very likely. I hope you can get a fast turn around on the service.