As of yesterday, I am now experiencing the "Unable to browse music" message when trying to use Libby by Overdrive with my Sonos system.  I have read through the replies found here and tried the suggestions provided.  Unfortunately, I am still staring at the same message.  Has anyone found a workaround for this problem?  Moreover, one has to wonder why Sonos and/or Libby have not yet addressed this issue?  Looking at this thread, it has been happening for over 3 years.  Surely this is not what they see as good customer service.

Do a validate of the Libby plug-in. Mostly works.

Yes, Sonos blames it on Libby, and vice versa. Libby plug-in also has a problem reporting current book position. Sometimes takes up to a day to report to Libby website, and when it does, you have to go to the actual Libby App to accept the new updated book position, otherwise Sonos Libby will start again at the old position.

Thanks for your response, @fischershaw.  I validated the Libby app on my phone yesterday and, upon seeing your response, did it again.  Here is hoping… 

I still cannot understand what happened.  I had just finished listening to an audio book using Libby via Sonos, something that I had done numerous times in the past without any problems.  I returned the audiobook to the library and deleted the item from the “Recently Played” screen in Sonos.  I then went to start listening to another book via Libby by Overdrive in Sonos and there was nothing there except the “Unable to browse music” message.  Here is hoping things get fixed soon.  In the meantime, take care and thanks again.

Further to my post yesterday, I am happy to report that I no longer see the “Unable to browse music” message when I open up Libby by OverDrive.  Instead, I see the book that I signed out from the library.  Woo hoo.  Thanks again for your help, @fischershaw.  I think revalidating the third time might have been the charm.