error opening recording device 9996 unanticipated host error

I am trying to use a BOSS AD10 acoustic preamp via USB for recording. When I connect this device, and click on monitor recording level I get the above error code/message. Any advice why this is happening? Incidentally, I cannot get this device to work online with Jamulus either. I am using a piezo contact microphone - all works fine through my amp! I updated Audacity from 2.3.1 to 2.4.1 with same result. Settings in Audacity are:
WASAPI audio host/IN=AD10/Mono recording/Headset Earphone as playback device. What am I missing??

And as if by magic, with a reboot, all working fine now! :smiley: