m$ servers are busy at the moment, check also if the correct key (the same for all) has been implemented or try with slmgr / ipk XXXX
Had the same type of message on a preview build, had to use phone activation. The first person had no clue, referred me to a supervisor who helped me complete the process.
just in case.. set DNS to google 8.8.8.8 8.8.4.4 and run adwcleaner. sfc /scannow cant hurt either. might have to refresh if days go by and same.
Hope you haven't fiddled with the services/msconfig. I disabled a few services before connect to the net and it won't activate until i set the services back to default, in my case i must have turned something important off but doesn't look important. Just an thing to watch out for.
You nailed that right on the head and you forgot about any traces of mocking up the original registry that will guarantee you a cookie and a glass of warm milk also