Have you tried upgrading on WiFi?

Others will chime in but simple things to try are before you run the update...

Power cycle the router

power-cycle the port

Plugging directly into the router (you did not specify how it gets it’s connection)

Replacing the Ethernet cable

Edit… good idea GuitarSuperstar

Did all that already a dozen times. But no avail. Even did it together with a sonos support representative but still same thing. 
It al started with the update of last week. Have reset the port, rebooted the router. Disconnect everything from the network with only the port connected. Always the same result. Stating: there was en error during the upgrade please try again. 

It’s a stab in the dark, but you might want to try updating from a different controller device, if you have one available.

Already tried from an iPhone, ipad and the Mac controller all show the same result. So the port is on sonosnet with wm0. With no other Sonos speakers connected (just to reduce complexity). And all other internet devices run as expected (hue, Apple TV etc). Even sonosradio is working. If I don’t upgrade after a reboot. But since I did a factory reset to the port I cannot connect any other speakers before an upgrade. So I need to upgrade before I can use the system. 
to me it seems that S2 is only bringing trouble. were happy with Sonos for more then 10 years but since I bought the port a couple of months ago and upgraded to S2 it seems as if the system is a lot less stable and sonos is no fun anymore. 

S2 is quite stable. What error code does the update fail with? 

No error code - it just mentions try again. 
After this the port is in error mode and a reboot is required to function again. Was last week for more than an hour on the phone with sonos support without solution they mailed a suggestion I also tried without succes and haven’t heard since. So no I am not happy with S2. 

Is there not a ‘more information’ link on the failure popup? 

Hi @H12543 

Welcome to the Sonos Community!

I recommend you get back in touch with our technical support team, who have tools at their disposal that will allow them to give you advice specific to your Sonos system. I also recommend you call rather than chat.

Corry,

Note that in the post two above yours, he mentions he spoke with support on the phone for over an hour. 

That being said, unless there’s a second level of support he can reach, I’m really not sure there’s much this forum can do. 

I’d certainly be tempted at this point to do a complete factory reset of the device, and see if there’s some current software issue keeping it, in the current state, from updating. I’d think/hope that a factory reset, while erasing all currently stored account information, might reset it so it can be updated. But, he’s already tried that, as indicated in his post above, so I’m at a loss. 

The whole situation is odd. I’ve been using S2 on my 20+ speakers since it was released, with absolutely zero issues, either in use, or when updates come out to apply.

Thank you for your replies. I have used sonos over 10 years without issues ...until now. 
After another hour on the phone last Friday. Support was indicating that some of my system  was still on S1 (although I updated the system in November 2020 to s2. Have again done a restart of my router, now have only a play 1 wired connected to the router. Start my s1 app → this indicates it is S2 software, start the S2 app and this indicates an update is needed. The update fails after more then 5 minutes showing getting started and I need to reboot the play1 in order to see it again in the app. 
So no until now contacting support has not been that helpful. 
Have a sonos system not working for over 2 weeks