[HP DesignJet T3500 series]

1. Use the power switch at the rear to turn off the printer, then disconnect the power cord. Reconnect the power cord, then turn on the printer.
2. Check that the network cable is correctly connected to the network interface.
3. Update the firmware.

If system error persists:

4. If the printer is blocked showing the system error persistently; check that the network interface card (including the riser) are correctly connected.
5. If the printer is blocked showing the system error persistently; replace the network interface card.