I worked at a school where we had many HP 4000 series printers deployed. I like these machines a lot, but they have started to develop an issue picking up paper from the trays. The machine will try multiple times to pick up the new paper, then give up with the paper jam message.

The problem is the friction clutch on the reverse roller mounted to the tray. It's easily repaired by removing some (but not all!) of the iron filings inside.