While in maintenance mode, press 8 and 2 to enter equipment error code indication (maintenance mode 82). (See previous step on how to enter maintenance mode.)

Cycle through errors by pressing the Mono (or Mono Start) key. Error codes 20 to 2D indicate problems which are probably related to the ink cartridge IC chip.

For a full list of error codes and their meaning you can also refer to the service manual, chapter 2.3.

Try to remove the error messages by removing and re-installing the ink cartridges.

If the problem is not solved, a resetting of the ink cartridge IC chip can probably fix the issue (see next step).