check your render settings; i know sometimes mental ray (i think its mental ray, might be maya hardware) doesnt render certain geometry types very well sometimes. there used to be a problem, im not sure if it still exists, with the subdivisions; if they had like a tri it wouldnt render the entire geometry. so check your render settings, geometry, and most importantly see what the Script Editor says after you render, if it mentions anything about your geometry or posts and Error message thatll help solve your problem