Do you have automatic updates enabled on your Windows PC? 
Have you followed the steps as outlined here?:

https://support.sonos.com/en-us/article/error-913-when-adding-a-music-library-share
 

So, I’ve finally managed to find a solution, I hope it may help many of you guys. Apparently windows aloud only a certain amount of active connection (10), and because of that it may appear the error 913 when we try to add a shared folder to the sonos music library. I found the solution opening the cmd (open powershell.exe with administrator rights) and tap the command “net sessions /delete /y” (without commas). This command will close all open connections and aloud you finally to add your music library on the Sonos desktop app. This command and the procedure for the shared folder in the attached picture should solve all your problems :)

It’s been over a year since the infamous 913 error began. The people that were held responsible for these disastrous software updates are now all gone. It seems to have gotten a little better (still major issues with iPAD app for example) but I am not convinced they are anywhere humming along like Microsoft Windows 11 yet (unlike Windows 10 which was a nightmare) to be relatively error free with constant updates. Until then, I will NEVER buy a new piece of Sonos equipment.

So I got my new 913 error with Sonos PC Desktop controller Version 17.1.1 yesterday again. Checking all the file sharing permissions were given to “everyone” and “Sonos” for the music subdirectory to be accessed did nothing. And the old Norton Firewall traffic rules have been replaced by a new “Smart Firewall” that there isn’t much checking and unchecking to do.

Randomly, I managed to find two things to fix. I went into Windows Settings Advanced Network Settings and had to check Network Discovery and File and Printer Sharing. Then also in Sonos PC Desktop Controller Music Library Settings under the Advanced tab, I checked Make Music Library Permissions.

REBOOT.

Then now it works. But how would anyone know?

Sonos may ask so why is it a Sonos problem? I would only say, if Sonos’s business model is a reasonable compromise of portability plus quality at a reasonable price, you have to try harder. Why do Audacity, Openshot and OBS Studio don’t have these problems (Audacity used to, but I think they have aced it since) and they are opensource and FREE.

Why so many people are no longer buying Sonos, myself included, is just the hassle. We would gladly even pay more if Sonos only works smoothly. Do I really have to revisit file sharing forever? I’d rather throw away all my old Sonos stuff.

The recent Windows update has an issue with the firewall. Try disabling it temporarily to see if you can connect to your library. I had to remove the recent updates to get my Windows PC working again because it would go directly to the BSOD.

My suggestion to you would be to get yourself a proper NAS for your music library. I use a Synology NAS and I never have the issues you are having.

Thanks.

BSOD sounds very grim as it should.

I’d rather get a real NAS than disable firewall or reinstall older versions of Windows.

I’m using Synology. Overall I like it. My only complaint is that it’s a bit slow to startup. If the drive has been sleeping, SONOS will time out while attempting to play the first tracks.

Yeah, they broke it on purpose a while back for ‘reasons.’

Huge numbers of Sonos users have lost access to their own internal Music folders and if you ever try to talk about it you just get aggressive responses from people who send you the same instructions that absolutely do not work.

If you don't like the suggestions from other users contacting Sonos Support is your other option.