Need Help

Hi there. I have a problem doing something. The first thing is that, I used "Membership.CreateUser" rather than "WebSecurity.CreateUserAndAccount" because it is a totally different framework than what am I using, so my professor recommended me to use Membership.CreateUser instead. But doing so, I always get this error: "the password-answer supplied is invalid". Here is my code:

var confirmationToken = Membership.CreateUser(username, password, email).ToString();
var confirmationUrl = "http://mikepope.com/testmembership/ConfirmAccount?confirmation="
+HttpUtility.UrlEncode(confirmationToken);
var confirmationLink = String.Format("<a href=\"{0}\"></a>", confirmationUrl);

Thanks in Advance.
...