Lexmark MX812
Install the missing fuser. For more information, see the instruction sheet that came with the replacement part.
From the control panel, touch Supply replaced to clear the message.
Here are troubleshooting steps for a ‘121.xx’ Service Fuser Error (except for 121.02. 121.16, 121.41 and 126.01).
Replace Cartridge Option Is Missing in Email Alert Setup List