Adjusments for avaibable

I am running Aperture 3 on a 2009 MacPro with 8 gigs of Ram. I have had no problems until now. Although info is available under the Library and Metadata tabs, when I choose the Adjustment tab, I only see is the histogram. The adjustment options/sliders are all gray. As far as know, I haven't changed a setting. Any idea on how to trouble-shoot?

Thanks.

Wm.
wmcy@mac.com