Nikon D60 will not let me set aperture ring on lowest number?

I have a Promaster Lens and whenever i try setting the aperture ring to the lowest number it tells me to set it to the largest number on the aperture ring. Why? D

The exposure meter is trying to tell you that you are going to overexpose the photo if you set the aperture on the lowest number. You can't just set any numbers you want into a camera and expect to get a photo. Shutter speed, aperture, and ISO all have to work in the correct values depending on the light in the scene.

I suggest you study this:
http://teenagephotographer.com/the-basics/

Your camera is in P, S or A mode. You should set (and leave) the aperture ring at the highest f/number (smallest aperture size) to give the camera control over aperture size. If you want to control aperture size yourself, use the control wheel. Read the user's manual for more details.