Best answer by Airgetlam
The other possibility is a duplicate IP address issue. The quick and dirty fix is to unplug all your Sonos devices (and anything else that connects to your router, if you can), and then reboot the router. Once the router comes back up, plug in the first Sonos device, giving it enough time to reboot as well. If you happen to have one of your Sonos devices connected to your router with an ethernet cable, do that one first. Then you can move on to the next Sonos device and plug it in, again waiting for it to fully boot. Repeat the plug in and wait sequence for all the rest of the devices that you unplugged.
There's a more permanent fix if you have this issue, which is to go in to your router's IP address table and reserve addresses for all of your devices. That would keep them from stepping on each other in the future.