ok makes sense.

Yeah I've used CMS a lot in the past - really beneficial. I've just never had to use one with SQL Server Auth before (special server that...

sorry - seems I edited my response after you made your post 🙂

Actually, it says

In the New Server Registration dialog box, select the instance of SQL Server that you want to become the central management server from the drop-down list of...

One last thing - if I use a SSMS earlier than 2016 and then connect to the 2016 CMS server and try and register a server I cannot even select...