I had a weird "freezes at adding objects" problem which I managed to get round. Whenever I had a scene that was rendering fine for the first render I did but always locked up on the second render, even when I reverted to earlier scenes that had previously worked. I took out elements from the scene till this stopped happening. Then I readded the last element, in this case it was M3, piece by piece till it happened again. Using elimination I discovered the culprit was part of the Poser 5 hair (layer 1). By recreating this bit I fixed the problem. Hope this helps.