Are you certain that Dork is actually close enough to the mountain prop that he can cast a shadow onto it? Poser figures can appear to be touching or very close to things, but if I check a side camera, I sometimes find that they're floating above it or are quite a distance away from where they appear to be. It helps to move them slightly into the prop, to the point that they're intersecting it, then slowly back them out in tiny increments. Don't know if this is your problem, but you only need to check the gallery to see how common it is :)