Select the prop, go to the Properties panel, deselect Smooth Polygons and set your Crease Angle to 20...now try another render.
If this doesn't correct it then you'll need to take your obj into another program and smooth the normal face angles.

Not saying this next statement to be-little you, just confirming with you that this is an age old problem with Poser, it can be solved but you have to know the dance steps.

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