Thanks for the additional info.
First, an apology: I misread the lens description, sorry. If you have the "AF 70-300mm f/4-5.6 ED Nikkor" then the lens DOES have an aperture ring at the rear of the lens. If this is the case, then your D50 is compatible and all you need to do is turn the aperture ring on the lens until it's at the minimum f32 setting. The "FEE" message on your D50 should then vanish. When set this way, you control the aperture setting on the lens via the camera body controls. The command wheel alone adjusts the aperture when in Aperture Priority mode, and in Manual or Shutter Priority modes you need to first press the " /-" button behind and to the right of the shutter release before using the command wheel. There's even a handy little printed icon of a lens diaphragm to remind you of the secondary function of this button.
If your lens model is the "Nikon 70-300mm f/4-5.6G" then like a G lenses it lacks an aperture ring and so can only be controlled by Nikon bodies which operate the aperture from the body alone, like yours. So if you're getting the FEE error with a G lens then there's most likely a common fault which occurs with Nikon bodies with a small switch beside the lens mount. In the picture (courtesy and copyright of Digital Photography Review
), the switch is at the 8 o'clock position.
This switch is activated either when a non-G lens aperture ring is turned to the smallest setting or when a G lens is correctly mounted. It is possible for the G lens to be damaged in such a way that the switch doesn't get activated but it's rare. If the switch is broken the camera body will need a repair.
Hope this answers your question, but if not add further comments. If it has answered your problem then please let me know by rating my reply.