Try removing/uninstalling the App and reinstalling the latest S1 App from the Sonos official download site here:

https://support.sonos.com/en-us/downloads

Then go onto connect back to your ‘existing’ local system and (if required) update the firmware on your Sonos devices.

If you’re a little sceptical about uninstalling/reinstalling the App, then you could also try this suggested fix…

MacOS Sonos controller App not updating…

Maybe try this … Authorise the “Sonos Installer” under System Settings → Privacy & Security → App Management. Once allowed, you should be able to use auto-update from the Sonos App itself.

Thanks for the tip. I enabled sonos as advised above and rebooted my laptop. But no change - it still complains about an unexpected error on install. I am wary of deleting the app and reinstalling because there is a danger that I end up without an app at all. (The current version does work, it’s just a couple of upgrades out of date...)

I’d think that danger extremely (less than 1%)  small. The only reason you could end up in that position is if your computer didn’t meet the supported OS for controllers FAQ. You might, in fact, merely rename the current version you’re running, and download the new version, and run it temporarily. If it didn’t work, you could delete the new version, rename the old, and likely run it still. 

But it’s certainly your decision. 

good point…

okay - that’s working. Strange through. And I had a similar problem with my spotify app - which thought I was not a paying customer. In both cases, delete and reinstall did the job. But that shouldn’t be necessary - it always bugs me when the regular route doesn’t work and you are left not knowing which 1’s and 0’s got in a muddle and why!
Anyway, thanks for your help.

Cheers

Tim.