Okay, I did find something interesting.  For some reason the runtime files for the fox and other models were put into Poser4 - since I've been putting files in Poser4 for a very long time, and Carrara6 just didn't like pulling from Poser4 for these particular models... When I moved the files for the problem models over to Poser6 Runtime, everything work.  Go figure.  Hope this helps anyone else who runs into this prob.

Never Give Up!