My W-Class printer will not print on my new Direct Thermal (DT) labels, but prints perfectly on Thermal Transfer (TT). Why?
Most likely, the media you are using is not DT media. Place a label on a flat surface and scratch it briskly with a coin or fingernail. If the scratched area changes color to a dark gray or black, then the media is DT. If you only leave a shiny scratch mark or there is no color change, the media is TT and requires a ribbon.