I'm no expert on lighting or Poser 5, but I agree wholeheartedly with amon_q ... delete the default lights before adding a light set, and make sure you delete lights rather than turning them "off." You may also find very satisfactory results with trying one or two lights rather than complex light sets. Poser 5 seems to allow for a delicate touch with lighting. I know not all lighting sets make Poser 5 go funky because I've used Les Bentley's Omnilights, Joaquim Ojeda's Special Lights, and 3DModelz's Volumeric Lighting without a problem. And, yes, I know my own graphics are not good examples of excellent lighting, but the point is that I haven't had Poser 5 crash because of lighting for many weeks.