I would also post this over on the MSDN forums. This sounds like an unusual problem that is probably related to your network. Do you have a proxy? You might try registering from a different computer on a different network then carrying the registration code over to your machine.
In the meantime, you should be able to install via the offline ISO download which I think gives you two weeks to use it w/o being registered. Hopefully, you’ll get the registration resolved during that time.
Thanks, guys, for all the suggestions. Managed to fix it myself when I tried this morning. Either the Microsoft server was having conniptions yesterday or else it regards email addresses as case sensitive! Typed my email address in in lower case (I usually capitalize it) and it went through fine.
Sorry to waste everyone’s time. Hope to see you around with more interesting topics.