PlanetCNC TNG software uses new and optimised USB driver.
In order to update and use your PlanetCNC Mk3 series controller with PlanetCNC TNG software, you would need to use latest PlanetCNC USB driver.
To check your USB driver version click: Win Key/Control Panel/Device Manager
Under connected devices you will notice CNC USB controller:
Right click on it and choose Properties, and under Driver tab you will see USB driver version:
You will notice that USB driver version is 188.8.131.52. and that it is not digitally signed.
You can get latest PlanetCNC USB driver here: PlanetCNC software download page
After you download file double click on the .exe file and follow installation wizard.
After installation is complete, it would be best to restart your computer.
Now check if your USB driver has been updated to latest version, click: Win Key/Control Panel/Device Manager
You will notice that PlanetCNC device has a new name: PlanetCNC controller
If you check properties of this device you will see that under Driver tab driver version is now 184.108.40.206. and is digitally signed by PlanetCNC d.o.o.: