I have the same exact issue, but I have already installed twice now and not so thrilled that I may need to do it a 3rd time. I have ALWAYS installed windows by passing the key during install and just using my 10 Pro key from within settings. THAT has always worked for me on Windows 10 Pro.

So why that same exact thing doesnt work here is just crazy. It does however recognize that it is a Insider Build 17713 and it seems to run great. I just wish it would let me sign into my Microsoft account somewhere or at least let me Activate it using the Standard key that was given to everyone. I can't even find a Feedback Hub to give feedback as it tells me I need to install it. Jeez

Oh well... I should have just dumped Server and used Ubuntu Server, that is soooooooo much easier.