Hi Mike,
Thanks for the response. I figured out the problem, and corrected it yesterday evening. I meant to reply to the post.
The problem was I had hidden the SHAPE field in ArcMap. When I made the field visible, refreshed the service and cleared the REST cache I was then able to engage the pop-ups.
It looks like the SHAPE field is needed to be visible for the ArcGIS.com Viewer and ArcGIS Explorer Online if you want to work with attributes. I had another problem with results being returned by Queries in ArcGIS Explorer Online. Without the SHAPE field I could not zoom to the results of the Query. With the SHAPE field I could zoom to the results.
Either way, everything is working fine now.
Thanks again,
Mike