As a result, I no longer have music. (and I'm leaving on a business trip so my wife will have no music his week. Am NOT amused with the Sonos Software team.) I did everything as prompted, the system appears to work, except that it can't access my music: the same music it COULD access on Friday. Sadly, this will have to wait until I get back next weekend, but I'm not happy with Sonos right now...
Best answer by Airgetlam
Try removing the link to your library, then quit the app, and then add it back in.
Then, if that doesn't work, go ahead and delete the app itself, and then reboot your Mac, and install a fresh copy. Since the data is stored on your speakers, the only potential change would be a reset of the pipeline to the library.
Finally, it might be worth it if you were to submit a system diagnostic within 10 minutes of replicating this issue, and either post the number here, or contact Sonos to discuss it. There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.