HERE'S THE SOLUTION....AT LEAST IT WORKED FOR ME.....

 

Unplug power box at rear of printer.

 

Open the printer as if you are going to scan a doc....obviously hook the tab so it stays open.  Using a flashlight locate the two black tabs far right and left in the rear that act as hinges.

PUSH BOTH HINGES TO THE RIGHT carefully while holding the cover (it will float free but will remain attached by the white ribbon cable.  Set the cover down to free your hands.

 

Just to the left of the white ribbon is a rectangular hole.  There should be a small plastic tab inside that you can move with your finger towards you.  Let it go and it should spring back into place.  This is the cover open sensor.  (If it's not there...that's your problem.  It broke off.)

 

Plug in power.  Hold the tab towards you.  The message screen should clear the cover open message.

 

Mine WAS there.  I moved it a couple of times freely.  Message returned to normal.

 

Replace cover making sure that black tab on cover fits into and moves tab into proper position.

Hinges pop into place at same time.

 

It took me longer to write this then to fix my printer.   Good luck.