Each time I connect using the machine control panel have to remember to click on the PORT selector and go to the bottom of a very technical looking list to select the one port that has the letters "USB" in it. Otherwise of course it won't work.
a) the software remembers the last choice made for a successful connection;
b) in the absence of (a) then the sofware defaults to the most likely choice given the OS (Mac, Windows....). Probably something to do with USB.