It usually happens to me when I am fooling with the lights--sometimes there is some weird conflict between the environmental lights, the camera auto light, and the ones we load in manually. Then poof! It doesn't seem to be like Poser, where Poser bogs down with too many polygons/textures. That said, V8 and her normal maps can hit 500 mb easy, especially when you add a complicated outfit. Try adding things one at a time and keep saving your scene.