try making sure the materials file has all of the correct stuff typed so if you have two diffrent sides*one side of the head is diffrent then the other* then make sure in materials it says under left preset_#headL.jpg and the right says preset_#headR.jpg, make sure the .jpg and most of all if the materials file says preset_#headL.jpg and preset_#headR.jpg and the heads arnet diffrent then get rid of the L and R.(i just used the heads as an example)