Cause

The ink has run out.
 

What to Do

Replace the ink cartridge and close the cover.

If printing is in progress and you want to continue printing, press the machine's Stop button for at least 5 seconds with the ink cartridge installed. Then printing can continue under the ink out condition.

The function for detecting the remaining ink level will be disabled.

Replace the empty ink cartridge immediately after the printing. The resulting print quality is not satisfactory, if printing is continued under the ink out condition.