Clear "paper jam" message

On a MFC-4420DW I'm attempting to print business cards on Avery stock through the rear, single sheet feed tray. Data transfer from PC is very slow, and when printing begins only the first quarter of image prints and sheet exits printer. Thereafter I get a Paper Jam message. I have followed the "clear paper jam" instructions several times, referred to online instructions, used a letter-sized sheet of glossy photo paper for the "remove paper scraps" function, but printer does not grab the sheet. I have closely searched the inside of the printer for scraps and can't find a thing. How can I clear the error message so I can use my printer again?! Frustrated!