Code 1101 is normally a connection error.  You don’t mention which Sonos products you have installed, can you let us know?  Is it possible to temporarily connect one of your devices to your router via an Ethernet cable and retry the update?

The other cause could be duplicate IP Addresses within your home network, if you’ve rebooted your router.  Please see my post here.

I have connect, playbar, sub, 2 old play5s, 2 play 3s, 2 play1s

What happened is all of my S2 compatible products “upgraded” to S2. I have no idea how this happened, logged into my sonos s1 controller on my pc yesterday and it only showed the 2 old play5s. So I downgraded all of the speakers/connect back to S1. But now I can not add any of the products back to my S1 based system. Add product is greyed out. I believe the system needs to update but i get the error code 1101. I have tried on 3 different devices, connected with ethernet cable, rebooted, etc etc etc.

So you followed: 

Downgrade a Sonos product from S2 to S1 | Sonos

Removed the S2 App

Installed the S1 App?

Yes.

A bit of a long shot but can you power down all your Sonos devices for about 1 min and retry.

Edit: Mixed metaphor! 

Otherwise, you may want to check my post: Tips & Tricks - Resolving random issues impacting Sonos devices.. | Sonos Community

It was in my first post but not sure if you tried the steps?

ok trying.

I find it weird that the S2 app had no problem updating but the S1 app will not. I am suspicious this could be an app update issue?

It could be, I’ve never downgraded a product to S1 myself!

I have all products unplugged and still get the same message when trying to update.

Is it worth trying “forget the system”?

Your system is stored on your devices so with all of your devices unplugged it won’t find anything.  Try plugging an old Play5 in and retrying.

Yes, just tried this, same result. Guess I will call Sonos again. Appreciate your time!

Did you try the actions in my other post?  Sorry, I couldn’t help further.

Hi, I worked with Sonos level 2 support, it was a glitch with their system involving S2/S1/app update/speaker update. I couldn’t follow exactly what they did from their end but they got it fixed. 

You may want to speak with all users of your Sonos. There is no process by which the system updates itself to S2, it requires someone to make that decision, and apply the update. 
 

Someone may have thought they were ‘helping’ by running that update for you, however they should leave the management of your system to you. In fact, you may want to change the password on your system, so that only you have the ability to access software changes.

I agree with this; however, we did not have any S2 apps installed, so if this update/upgrade was initiated by someone (wife/kid/etc.), it must have been initiated from within the S1 app (which I would suggest should not be allowed). Also, support said the root of the issue and where the “glitch” existed was with software in the old Play5s needing to be “locked” out of trying to update/run S2. Again, I don’t fully understand it, but if you have a system on S1 which only has S1 compatible speakers (how mine was set-up during troubleshooting) it doesn’t make much sense that you need to tell it to stop trying to run S2. Luckily support was able to get it working by having me go into the S1 App, do multiple system compatibility checks, and keep selecting “continue with S1” or something like that. 

Either way, someone had to initiate it. It doesn’t happen automatically. 

I agree, Sonos might be able to add code just to the controller, and not the speakers, to check to see if there are any S1 only devices, and pop up a warning, but they may already be limited on what they can do for space, if it has to live in both areas.