I upgraded an 8200N to a DP by switching out the board from another machine. The printer still prints beautifully in one sided mode but jams when trying to feed the paper in to print the second side. I have checked for obstructions and found none. I assume there is a sensor that is causing the jam. When I clear the jam and close the exit door the machine makes a horrible sound on the lefthand side and then reprints page one, after several jams it shuts off and restarts. Any ideas?