Why won't my Lync 2013 5.6.3.1 connect to the server?

A

AC Question

Lync 2013 5.6.3.1 won't connect to server

Same app on two tablets - Xperia 2 and Xperia 4. All details are correct as the identical config is on my phone but this is a different version. I have rolled back to a 5.4 version and it works on the tablet. So, is this an App issue or is there a compatibility issue with the Sony Tablets? Could there have been features added to the app that are not allowed through my company Lync server?

Thanks