I run across this problem frequently...the back side of the figure/prop won't render.  I've attached an image and you can see the background through the costume's head...and you shouldn't be able to.

I use PoserPro 2010.  It doesn't matter what light set I use, the angle/focal point of the camera or if I use indirect lighting.  Can anyone give me some pointers on how to solve this?  Thanks.  Dani