This error occurs if you try to generate a DCC (not publish a DCC) and the dongle is not inserted. If it is inserted you may have a bad USB port on your computer. Try another port or try another device in that port, like a USB mouse if you have one. Note that you CANNOT insert the dongle after you start MillMax. It looks for the dongle at start-up.
UPDATE: On rare occasion the dongle itself can fail. To test it, shut down your computer completely. Insert the dongle into a USB port. Start the computer and check to see if the light on the dongle comes on. If it does the dongle is working.
If you try to publish a DCC without a dongle, you will get this error:
