Lexmark X646
Intermittent 900 firmware error appears on the printer and scanner is too hot at some point.
Turn off the printer and power it back on after one minute.
Check the printer if the error message still appears.
Check the surface of the scanner and verify if becomes too hot.
298.01 or 298.02 Scanner Missing Message on the Lexmark X782e Color MFP or X646ef Laser MFP
Here are steps to clear a '29x Scanner Jam' message on the Lexmark X642e, X644e or X646e multifunction printer.