Quote - thats odd. I  use Poser 7 and have done scenes with 2 V4 and 4 m3/m4 characters. Renders are not fast but it does do it.

as others have said, use RR figures for background , render in layers and composite in photosshop, render and create your own billboards.  

Be careful with high res textures if they are not required. 

I confirm what you say. I could also have more characters with Poser 7, depending on the morphs, clothes and textures I used. But since I have PoserPro 2012 I can no longer even open some of the scenes I created in Poser 7 with 3 M4/V4 characters. And those I can open won't render with shadows.