Might not be a memory problem. Sometimes Poser gets confused and the scene becomes unstable (this might have happened in any saved version). My advise would be to reboot, construct a simple scene first, render it, save it, load it and render it again. Then start building from scratch. This worked for me several times. I never had a persistant problem with any scene in Poser. Complex scenes just become terribly slow. Pose each figure separately, save as a character, reboot, start Poser and move each figure in, then render and wait and wait, finally something happens and the screen starts building up.