Alicia, the D70s detects whether an AF-D lens is set to minimum aperture differently than the D300. In the case of the D70s there is a little switch located at about the 8 o'clock position around the body lens mount that is activated by a small lever on the lens mount. The D300 doesn't have this little switch and detects the minimum aperture differently. I'm not sure exactly how the D300 senses the lens aperture except it might be the AI indexing lever and maybe electronically.
One thing you can try is to use the aperture ring to set the aperture instead of the front command dial. This is set by f7 in the Custom Setting Menu. Change Aperture setting from ON ---> Sub command dial to ---> Aperture ring. Then unlock the lens aperture ring from f22 and adjust the aperture via the ring. See if the upper control panel display matches the manual aperture setting. See if it can be set to f22.