I checked. There is no sheet of any kind inside or below the door of my Whirlpool dishwasher.
In any case, opening up the non-washing washer revealed that the filter behind the chopper assembly was clogged with food. I cleaned it off, put the thing back together again, and it was washing dishes again, until about three days later. I took it apart again and found food clogging the filter behind the chopper. I thought the chopper wasn't chopping, so I replaced it. It was around $16. About three days later it wasn't washing dishes again.
Further examination (dis-assembly of the sump motor and impeller) revealed that the end of the impeller (which is designed to engage the chopper) had broken off, thus the chopper no longer spins with the sump motor. The impeller costs about $20 and isn't too hard to replace, as long and you keep track of what you've dis-assembled and put it back together in reverse order.
On whirlpool dishwashers, the sump motor drives the impeller (it's connected via the threaded end of the motor shaft) and the impeller, in turn, drives the chopper. The chopper you can replace from inside the tub, without removing the dishwasher from its home or taking apart the sump assembly. But save your $16, as that probably isn't what is wrong... The impeller, being screwed onto the motor shaft, requires complete removal of the dishwasher so that you can completely remove the base assembly that holds the motor assembly.
If you have a GU-series whirlpool washer, the tech manual can be found here:
https://secured.whirlpool.com/Service/SrvTechAdm.nsf/2cd44500d572193285256a45004fd9d6/52521bdbd0ef763c85256cbc00520548/$FILE/8178022.pdfIt has complete instructions for the replacement of every part.
