Maclean, I didn't mean you had to use the default GROUND plain, I just meant put a square under what ever you are using for the "ground". Actually what are you using for the ground/floor? If you are using a square try replacing it with as solid figure, a flattened cube, and you will probably find that the more depth the cube has the better the shadows performe. There is no "min shadow bias" in Poser 4, don't know about PP or P5.