Hard to be sure, based on the limited information. Are both of the surrounds One SLs? If they are, try a simple reboot of the router to see if that fixes it. Your Arc is what the surrounds are trying to connect to, and you have that hard wired, which reduces potential issues, so my guess is either the router isn’t properly providing an IP address through the Arc, or there is some sort of 5Ghz interference somewhere between the Arc and the surround speaker in question. 
 

It might be worth ‘sneaking up’ on the problem by setting up the two One SLs as separate rooms, and then moving them in to surround status, I’ve seen cases where that works, but unfortunately you may already have that situation, so it’s only a suggestion. 

Hi and thanks,  I managed to get it working but even though my arc is hard wired my rears are connecting to the q box wifi and all I can think is its because I have a sky mini box upstairs on WiFi and thats causing the problem , trouble is if I turn off 2 4 and 5 hertz on the q box I can't use the mini.

Ok, there’s some information there that’s somewhat concerning.  I would bet your assumption is correct, and some devices are trying to connect to one signal, and the others are in another. Just to confirm, your Arc is wired to the base Sky unit (the router) with an Ethernet cable, correct? If so, you should do two things.

First, make sure that the switch in the controller for WiFi on the Arc is turned on. It’s necessary for it to be on in order for the surrounds to be able to connect to the Arc. Surrounds do not connect to your WiFi signal, they connect to a signal created by the Arc. If that signal is turned off, the Surrounds can’t connect. 

Second, you should also be sure to be sure to remove Wifi data from your controller,  by following the instructions in the linked FAQ. This will force all of your Sonos devices on to the SonosNet signal being created by your Arc, and should allow you to run both the Sonos, and your Sky mini box upstairs. You’ll just want to make sure the two systems are using separate channels, as discussed in the the wifi interference FAQ.