I recently changed from a WD MyBook to a Synology NAS.  I can access the Synology Music folder from my computers, phones, etc.  I cannot add the music library from Sonos.  I have the logon and password entered correctly.  I am getting a 900 error.  I have increased the IRPStackSize to 24 as instructed elsewhere in the Sonos Community.  I have added a user (“Sonos”) on my Synolgy DSM.  Still no success.  Any suggestions?