What is the error message? Where is your local music library located? NAS, PC, Mac, other? Is it set up as an SMB v2 or v3 share on your network?
Have a look at this and see if it helps: Add your music library to Sonos
If not, Sonos support can probably tell what the problem is and help you resolve it. Try submitting a diagnostic (Submit Diagnostics) within 10 minutes of getting an error. Then call Sonos Support (Sonos Support) to discuss it. They may be able to see what’s going on since they have access to information about your network and sonos system that no one here has. Don’t post the diagnostic number here, though.