Try rendering a new scene with just the basic model (bald).  If it renders then load the problem render, model stripped, does it render, add the clothing, does it render, add the hair, does it render, if it fails, there is something wrong there.  Eliminate hair portions until it renders, then add until it fails, that may be your problem or try another hair piece.

I don't have Poser 8 yet (its coming--someday).  I have Poser 5 and the same thing happened to me and it was a certain part of the hair that did it.  When I deleted that part, everything worked. 

Just because a scene render perfectly, when saving it, it may not save stuff in the same place on the disk that it did.  Computers use the- throw -stuff- in- the- attic, closets, etc, there is a visitor coming method and it may have problems collecting all the stuff again.

Jan