First, physically remove the drum and verify there is no master attached. Check the for jams or broken transfer belts, which can prevent the master from leaving the drum area. 2. The "Sharpie Trick" (For False Errors)

: Wipe the small black velvet strip (usually near the clamp) with a dry cloth to remove paper dust.

: A used master master is actually stuck on the drum or failed to eject into the disposal box.

: Some users find success by placing a small piece of matte black gaffer tape over the strip to improve light absorption. 3. Reset and Service Mode

: If using an aftermarket screen, use a black permanent marker (Sharpie) to darken the entire black strip and the area around it to ensure no light reflects back to the sensor.

: The machine uses an optical sensor to detect masters. If the sensor is dirty or blocked, it may falsely report a master is present.

If the error persists on a clean drum, it is likely an optical detection issue.