Troubleshooting network connection errors on your Squeezebox is hard! Once the Squeezebox Duet is fully configured it is important to remember that you actually have two devices connected to your network: The Squeezebox player/receiver and the Squeezebox Duet controller!
If you eg. change network provider, router etc. you can easily set up your controller again, but you will have a very hard time reconfiguring or connecting to your Squeezebox receiver SBR as it is still configured for you old network!
In many troubleshooting situations the easiest and fastest solution is to do a full facotry reset and reconfiguration (as the full setup only takes about 1-2 minutes). Follow the steps provided here!