I'm happy user of GX680III and now not so happy with the Polaroid back I bought second hand from ebay. The GX680III doesn't fire the shutter with this Polaroid back. I'm guessing now the Polaroid back is older version and is not compatible with GX680III which thinks the film back is not ready. The Polaroid back has no electrical contacts or whatever unlike the film back (IIIN). Is there any way to let my GX680III just fire the shutter? Or am I wrong somewhere else?