Attempting to get Username given the UserId (Instead of the other way round) I keep getting a null reference

String userName = Membership.GetUser("ccb6e615-0ad7-4284-8984-3eb4fe82ae83", false).ToString();
 
thats does work
 
this doesnt work:
 
  MembershipUser User = Membership.GetUser("ccb6e615-0ad7-4284-8984-3eb4fe82ae83", false);
User.ToString()
 
or this:
 
User.UserName.ToString();
 
nor does it work when i set the boolean to true.
 
nor does it when I take the boolean away.
The userId exists, I know this for sure.
 
Also, This website keeps giving me errors, I tried to search this forum about this problem and it doesnt let me. Also, I was loged into windows, and it wouldn't even let me register - kept sending me to an error page. So I Logged into linux and it let me sign up but still wont let me search the forums.
 
Windows gets paid!
 
...