DIAGNOSIS You are getting a 'Document Jam' error on the scanner glass. This is almost always caused by a failed or dirty Automatic Document Feeder (ADF) sensor.
FIX 1. Turn the printer off and unplug it. 2. Open the ADF cover and locate the small white plastic sensor flag inside the paper path on the left side. 3. Clean the flag and the sensor slot with a dry cotton swab. 4. Manually move the flag to ensure it springs back. 5. Plug in and power on the printer.
IF THAT DIDN'T WORK The ADF scanner carriage might be stuck. With the printer off, manually slide the white scanner carriage under the ADF from left to right and back to ensure smooth movement.
HEADS UP This error is specific to the scanner, not the printer paper path. Do not disassemble the printer rollers for this message.