Thank Uli; I'll give that a try.

I made a little discovery; I opened a scene (very similar to the one above) that has never been able to render before at all in Poser 6 (either with FireFly or the Poser 4 engine) in Poser 4.03. It rendered just fine!!!!

This would lead me to think that either:
A) Poser 6 has a problem with it's rendering engines as the same scene on the same files/content works just fine in Poser 4.03
B) There is something in the runtime folder that is giving Poser 6 a problem, possibly left over from Poser 4.03 (All of my content is in Poser 4's runtime directory - it's what I was using before I got 6).