As I just said, I have a problem with Membership.CreateUser and Umbraco

I have a function that creates a user. The user gets created as supposed in the members section, but for some reason I cannot login.

If I go to the Umbraco backend and save the member, without changing anything, I can now log in with that member. Anybody got any idea on what to do?

CreateUser
_newMember = Membership.CreateUser(username, clearPass, email);
Roles.AddUserToRole(_newMember.UserName, "ForumUser");
_newMember.IsApproved = true;
Membership.UpdateUser(_newMember);

var document = new Member((int) _newMember.ProviderUserKey);
document.getProperty("forumUserPosts").Value = 0;
document.getProperty("forumUserLastPrivateMessage").Value = document.CreateDateTime;
document.getProperty("forumUserIsAuthorised").Value = true;
document.XmlGenerate(new XmlDocument());
document.Save();