I have been trying for the past WEEKS to accomplish that registration. I even created a brand new xbox / live / passport account and I always get that credt card error. But I am also getting alerts from my credit cards (I tried several different ones, with no positive results) that a succesful 1 euro transaction happened. So, the checking part works. It's the website that gets it wrong
The only help that I could get from MS Support was "try using Internet Explorer 9", which I did, and the result was the same!
Has anyone of you actually been able to complete registration?