My officejet pro 8020 will not print envelopes even when #10 envelope is selected on the printer

[rondamo]

My officejet pro 8020 will not print #10 envelopes even when they are selected on the printer and in the printing app. It gives me an error that the paper size detected by the printer does not match the paper size selected (Letter 8.5x11).  
I have gone into the printer and selected #10 envelope and have selected #10 envelope in the printing app.  I have unplugged the printer for 60 seconds and plugged back in.  I have taken out the envelopes and printed other items on letter with no problem.  This printer is only a year old.  How do I fix this?  Is there a way to bypass the error or a work around?

[AntoniosGrift]

Pull out the input tray, and then slide out the paper-width guides.
Load up to 5 envelopes print-side down with the short postage end toward the front of the tray.
Slide in the paper-width guides until they rest against the stack of envelopes.
Push the input tray into the printer.

Regards,
Peter