HP Laserjet 8100

[ICM Engineer]

Users are getting an error message on the control panel when trying to print to a network printer.
The error is shown in the title as Paper Jam.
The printer has been thoroughly checked and no paper jam found. Paper Path tests have been run on all input trays. Tested OK.
Switched off printer. Disconnect Jet direct card. Remove and re-install Jet Direct card. Does not remove error message.
What am I missing.
Are there any diagnostics that can be run.

[Placebo]

What is the exact error code? Did you test the manual feed tray also?

[DaFoerster]

I had this issue once where a user had tried to clear a paper jam and left a very thin piece of paper in the paper path that was totally undetectable until I used a flashlight and just so happened to see a very small piece of the paper looking up through the paper input path. It may be a faulty sensor, or a flag may be stuck as well.