Using Vegas Pro 16, Build 307

I would like to record audio from an external USB mono microphone, but am unable to turn on the "Arm to Record" button in the track header. It stays greyed our, as does the command in the right click dropdown menu. The Windows Audio set up shows that the mic is working fine.

No matter how may clicks I give the Arm Microphone button, it stays greyed out and does not turn on.

How do I arm the Arm button????