Step 1: Look at the Culprits - tabs on Fuji FP100 film pack

Step 1: Look at the Culprits - tabs on Fuji FP100 film pack, originally uploaded by peta-W.

Step 1: Look at the Culprits - tabs on Fuji FP100 film pack

in Polaroid camera / filmback view of Fuji FP-100B/C/3000B filmpack.

The "solution" involves placing bobby pins on the door side so that the spring levers of the back do not press on these "tabs" (see red rectangles in photo) any more -- the tip of the bobby pins may still press on the back of the packfilm cartridge, but as long as the pressure points are not against these 2 "tabs", then you should be OK.