Hi Robert,
I’m a user like you, not Roon Staff, and well remember feeling frustrated when Roon didn’t work straight away for me. Fortunately when I came to this forum other users were able to quickly assist in getting things going. That kind of mutual assistance is a continuing tradition here, I regard it as paying forward for the help given me.
There are also Roon staff who will look into the thread, this syntax - @support - will flag this thread so they see it ASAP. In the meantime you may find other users dropping in and trying to get things working for you.
My first thought with that message is that you have some other software running that has exclusive control of the device or hasn’t properly given up control of the device you are trying to send audio to. I’d suggest closing down all other audio programs, rebooting the computer and see if that helps. You might also click “Exclusive Mode” in the Settings/Audio setup cogwheel for that device. That will let Roon exclude other software from using the device.
If that doesnt solve things then it will assist Support to investigate if you can set out details of your hardware and software setup.
In relation to setting things up generally, the Roon Knowledge Base now has a User Guide section that can help avoid issues going forward.
Hopefully the above might get you hearing music, but if not then Support will be along shortly to investigate.
Edit: I saw this earlier post of yours which seems to be the same or a similar issue. Has your setup changed since then ?
Are you still using HQP ? If so, as Jussi mentioned, it wants to have exclusive control of the audio device.
Roon itself can share control with other audio programs (unless it is in Exclusive Mode), provided none of them demand exclusive control. It seems likely that another program you are running is insisting on taking exclusive control of the audio device.