The same thing as Costanza happened to me the few first times I tried to register, gave up and tried again a few days later and it worked, I didn't think about reporting this though since I thought it was now fixed. I really don't see what could be causing this.. temporary bug (?)
All I can say is that it doesn't seem to relate to what is entered in the registration form because I entered in a lots of different information over 10 times and the next time I typed in the exact same things as on my first try and it worked. Might be on the client's part too.
Anyway, I know nothing about networking so I'll leave this up to you guys, just reporting what I remembered.
This is weird. o.O