Message: Lock lens aperture ring at minimum aperture (largest f-number) I think I'm doing this but the message won't go away and the camera won't work.

You must lock the aperture ring to f/22, so the camera can engage the aperture adjustment lever on the lens. Then, you can change the aperture with the command wheel.

When you change the aperture with the command wheel the aperture ring on the lens doesn't move when the camera actually adjusts the lens aperture.

Take the lens off and locate the aperture adjustment lever on the lens mount.

Unfortunately, this won't work with older AF lenses. So if you are using an older lens, the only thing you can do is change the camera setting to M (Manual) to adjust the aperture on the lens yourself.