Have had this problem on my D80's. If you wiggle the lens back and forth in its mount (there is a slight amount of play in the lens to camera mount), clockwise/counter-clockwise, can you clear the ERR display ? If so, I would suspect the dirty/corroded contact issue. If it comes back quickly, I would suspect you need some type of anti-corrrosion material on the contacts. I can't say what to use, but others on this site have noted the same problem. Using alcohol as a cleaner apparently can increase the problem due to an increase in corrosion of the terminals. When it happens to mine, I just do the above (wiggle) and the problem goes away for quite a while.