Double check that there wasn’t an update to you NAS firmware that turned off SMB v1.

Here is an update. Airgetlam, yes, you are correct, Western Digital (WD) had an update to their firmware. When contacting WD, they responded that this issue was elevated to their engineering team for review. Yesterday WD had another firmware update. After installing it, Sonos can connect to my music library again. All is good now. 

You should have the ability to go in to the WD settings yourself and turn back on SMB v1, should it happen again. I’ve had to do it a couple of times on my WD device. Just took some research to find where they’d hidden the setting. 

I had troubles with connecting to my WD EX2 Ultra NAS drive after updating to the newest operating WD system . I chased the problem around quite a bit & followed the instructions for Error 900 & edited the registration entry to include the appropriate information, this did not resolve the problem. The solution came when I explored the settings in the WD NAS drive & was going through the “Shares” . When I went into the “Public” share it already had named the share as “SONOS” & so when I then chose this as the profile in the Music Library area & gave it the appropriate password all was resolved. I get the feeling that I would not have needed the Error 900 edit but having done that I was not going to go & delete as all is working well now. I also noted & SONOS folder was created when updating the NAS operating system so have moved a copy of my Music Collection into that. This was initially done to try & resolve the access issue but having done it I decide it was an easy way/place to identify so have left it at that option & will probably delete the original Public/Music Library location I had used.

All the SMB v1 options etc were already at the correct setting on the Public Share profile.

I hope this might help others experiencing the same issue after updating their WD drives to the new operating system. The update is a necessity if you want to continue normal access to your WD drive for other computing functionality as well as SONOS access as OS3 was not functional anymore. The WD update was easy the re establishment of the SONOS library a little more difficult.