Since I haven't had any responses and so I decided document what I have done so that it may help someone in the future.  I removed the toner cartridges, the imaging drums, the transfer belt, and the thermal fuser unit.   I noticed that behind where the transfer belt slides in, near where the yellow toner drum slides into the printer, on the back metal wall, a small plastic device ( approx 1 inch by 1/3 inch) that clips onto the metal back wall via three small slits was loose and not connected to the metal wall, but was just hanging there.  It took some doing but I was able to get the device to clip back into the metal wall.  After reassembling, the error has cleared.