Scara36. Take the time to fill out your profile so any of us can see what you have. Your friend may well have a 55-300 mm Dx zoom which is not a bad lens at all and is indeed an AF.
I shoot locally with several friends who have a variety of older N lenses, the 70-210 is among them in a couple of configurations and their lenses work well on the D300, etc. Could be the contacts as others have suggested. Or maybe you have the f-stop misadjusted, also as suggested earlier in another post. Good luck.