Sonos has screwed up their update process a few times. What happens is that they publish an XML file showing that a new update is available but forget to publish the update itself on their servers. Since the update check is a mandatory part of the installation process, they effectively lock out new customers from using their software. This most recently happened with the 4.2.1 update for Mac.
There’s a way to bypass this: redirect the site “update.sonos.com” to 127.0.0.1 (localhost) using your system hosts file. When you launch the Sonos Controller software for the first time, it will try to connect to your own computer to get the XML file. Instead, it will fail to connect and then move forward in the setup process. After that, you can re-enable access to the updates server.
The exact entry you want to add is:
Be sure to remove this line after you’ve gotten your system setup so you can get updates in the future.