I would suggest unchecking Smooth Polygons. It sounds like that is the issue.

Just to check: This doens't happen when you render anything on Poser's default ground plane, right? It's only when you use some other kind of floor?

FREEBIES! | My Gallery | My Store | My FB | Tumblr |
You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.