The FEE for Not Locking the Aperture
If you have a Nikon auto-focus camera and the display blinks 'FEE' at you, it doesn't mean it's time to put another coin in it in order to keep shooting.
For current Nikon bodies, the lens must be locked at its smallest aperture, typically f/22. You then adjust the f/stop by means of the body's command dial. Even on older auto-focus Nikon bodies the lens must be locked if you are shooting in shutter priority or program mode. If you don't, the lens lets you know by displaying the infamous 'FEE' error.
If this is the case, you may wonder why Nikon even puts aperture rings on their lenses these days. Nikon, too, has probably been wondering about this as they have started releasing some newer Nikkors as "G" series lenses which lack aperture rings completely. This completely prevents the problem at the expense of full backward compatibility to older bodies. Unfortunate, but it seems they have to make room for VR and other enhancements.
I don't really know whether 'FEE' has any literal meaning or not ("F/stop Exposure Error" maybe?), but at least the solution is simple once you know what the problem is.