You’ve checked the encoded files match the supported audio formats FAQ? 

Only thing here you didn’t do is reboot the router.

https://support.sonos.com/en-us/article/unable-to-add-tracks-to-the-queue

I had to re-encode a few of my FLAC files to Sonos supported formats to get them to play.

Yes, FLAC 16bit.  The Sonos PC app will also stream these files directly from the Windows PC without issue.

I did pull the plug on the router as recommended.  This, of course, did nothing to resolve the issue.

I’m not aware that you can stream directly from the Media Player App, you need to use the Sonos Library function, along with the Sonos controller app. As evidenced by your statement : The Sonos PC app will also stream these files directly from the Windows PC without issue.

Yes, the Sonos PC app has the ability to select a local folder and stream those files to the speaker.  That does work.  I am not trying to stream from Windows Media Player on the PC.  What is not working is when I connect to the to Media Server running on that PC from the Sonos Android app.  It sees the server, and will list all of the albums, artists, etc.  Selecting a song (or album) from there is what is giving the 701 error.  They ultimately point to the same FLAC files, so I assume the files are ok since the PC app plays them fine to the Sonos.

Apologies for misunderstanding. 

That’s really odd, I think. The Sonos controller is essentially connecting to the Sonos app running in the individual Sonos devices, and telling them what to do. There shouldn’t be any difference in anything between the PC app and the Android app, they’re both supposed to be connecting to the speakers. It’s even more odd that you’re getting an album list, but then they aren’t playing the file properly.

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

You might try disabling the Windows firewall and see if it is getting picky about connections from external devices that aren’t made from an internal source.

To wrap this up.  I talked to Sonos support.  Using Windows Media Player as a music server is not supported.  If I run the Sonos PC app and set it up as a server it does work, and by work I mean I can see the Sonos Music Library on the Android app and stream music to the speaker.  Apparently it is a codec issue which their app handles.

Thank you for all the input.  I’d still like to find a simple NAS type solution that does not involve Windows, any recommendations for that would be helpful.

Any NAS would likely do, as long as (and I think they all do) it supports SMB v2 or V3 (for S2, SMB v1 for S1). The NAS doesn’t really care what machines you connect to it, be they Windows or Mac, or Linux, it’s just a convenient way to manage all the settings that may or may not need to be changed. But ultimately, your speakers will be connecting directly to the NAS through SMB, and not going through your desktop.

I kinda like this option:

https://stan-miller.livejournal.com/940.html

Personally I use the NAS option I posted there.

$15 Pi, a few spare parts and you have a serviceable Sonos NAS,