Check your firewall settings:

https://support.sonos.com/en-us/article/configure-your-firewall-to-work-with-sonos

Thanks I've tried these steps and it gets the same error. Doesn't work still

I actually had my music library working (at last!) but after updating the Mac desktop app today now get the 1002 error message, and re-adding the library is failing despite the path being identical to what previously worked…...

Are you using the Sonos app on Windows to add the share?

​@MoPac yes its windows. 

I am using the same paths and settings that previously worked.

windows desktop > hardwired to ethernet switch > hardwired to router > full fibre

cheers Matt