No obvious paper jam but error message still appears

[E235]

My printer is HP LaserJet MFP M477fdw.  It is 5 years old.  Received error message "Jam in print paper path. Open rear door and clear jam." Did this and removed one piece of paper from rear.  Restarted printer but error message still shows.  Checked rear multiple time and no obvious signs of large or small pieces of paper. 

Things I have tried: 1) Restarted multiple times. 2) Removed and reattached power cord. 3) Plugged power cord directly into wall socket. 4) Updated firmware. 5) Tried print and scan doctor. 

Error message still shows.

Any help greatly appreciated.

Thank you.

[Valsimot]

If before paper jam printed a duplex job make sure you remove the paper tray, pull the green tab (inside the printer just above paper tray) to lower duplex tray and check for any paper.

[E235]

Thank you for your prompt response.  I tried your suggestion and was able to lower the duplex tray but there was no paper visible.  I restarted the printer and got the same error message.  Any other suggestions?