The "shadow" you see in a pre-render is not a shadow, its more like a placement guide. First of all, check that your characters and stuff in the scene is actually set to cast shadow, and also in the render settings, the Cast shadows must be ticked. Are you using raytraced or mapped shadows? Mapped shadows can sometimes dissapear if you have a large object in the scene (you can overcome this by choosing a larger shadowmap)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.