Broken or melted ribbon
Darkness is set too high.
Incorrect burn temperature.
The printhead or platen roller may be installed incorrectly.
Verify, if you can, that they are installed correctly. If necessary, call a service technician.
The printer does not detect when the ribbon runs out.
The printer may have been calibrated without ribbon or without the ribbon loaded properly.
In thermal transfer mode, the printer did not detect the ribbon even though it is loaded correctly.
The printer indicates that ribbon is out, even though the ribbon is loaded correctly.
The printer was not calibrated for the label and ribbon being used.