If registration continues to not work, there is a category of Tech Support Request devoted to bad registration. I did this using the online form and got a response within 24hrs. Considering Arturia is in France (5hrs ahead), that's not bad.
Look for replies to this online form via your My Arturia account. I never got a copy in my gmail inbox.
http://www.arturia.com/myarturiascroll down to My Support
Look for a case number in tiny font. I was able to click the number.
This sent me to Arturia's FogBugz window which had a message from Tech Support. Without a reply button.
To reply, compose an email to:registration-inquiry@arturia.com. Don't hit send just yet.
I copied the subject line from the FogBugz window verbatim. This should make it easier for them to sort through and find you on their end.
Don't be rude. Seriously. It seems like they take care of customers who aren't nasty to them.
Wikipedia suggests Arturia has a whopping 35 employees total. I suspect that as Arturia grows, their tech support and customer service side will improve quite a bit.