"If your USB devices switch which ports they are connected to the computer in, then that confuses Cakewalk. I suggest you try going into Cakewalk Preferences, and explicitly removing the A300 midi controller as a MIDI Input device and as a MIDI Output device. Then click Apply.
I would then exit Cakewalk, and relaunch it. Then, add the A300 back in again - and that should hopefully restablish its connection to Cakewalk."
Thanks for the help Robert!
I also changed USB cables and it works now!!!