"Pen Change" error message on HP Deskjet printers

When using the Linux HP Inkjet drivers (hpijs) and Common UNIX Printing System (CUPS) with some HP Deskjet printers (i.e. HP Deskjet 5650), hp-toolbox sometimes reports the less-than-illuminating "Pen Change" error message. Thie message actually means that the top cover of the printer is open or ajar, and needs to be closed.