Customer could only print one job at a time before error code came up. I found the following post that mentioned wrong default paper size and paper tray sensors causing this error.

http://h30499.www3.hp.com/t5/Printers-LaserJet/hp-laserjet-4000-41-3-unexpected-paper-size-help/td-p/1118558#.VG-n4snwtfc

We changed the printer paper size to “plain” and seated the trays till error disappeared.

I hope this helps someone else…