So, this just happened to me - and I wanted to share my experience. I got your error just as in this post: No sound
When this first happened, I plugged in my Bluetooth headset H10, then went back into audacity. I started playing, but of course audacity was playing through my earbuds which were sitting on the table, not my headset, so I couldn’t hear anything - duh! So I did a Transport > Rescan, so Audacity would know about my bluetooth headset. Instead of adding the headset to my available devices - it blanked them all out! (I don’t recall if there was an error message at this point). So I’m thinking what the …!
So I exited Audacity and restarted it and got the message on the above referenced post. No joy! Then I “Disabled” my bluetooth headset (as I recommended trying in my post above) - still no joy - AND WIndows continued to use it as my default output device - while it was disabled! I ended up powering the headset off.
I have no idea what happened! I powered the headset back on, re-enabled it and now audacity and everything else is working just fine. And audacity can play through my H10s bluetooth (as it once did in the past). Go figure! 