reset password

I am trying to have users reset their password using this method i found here:
http://peterkellner.net/2007/02/15/resetpasswordaspnet/#comment-598
  
'Dim user As MembershipUser = Membership.Provider.GetUser()
Dim user As MembershipUser = Membership.Providers("AdminMembershipProvider").GetUser(Context.User.Identity.Name, False)
Dim tempPw As String = user.ResetPassword()
Dim userFriendlyPw As String = "abc123"
user.ChangePassword(tempPw, userFriendlyPw)  I keep getting the null reference error. I am not able to reference my user.
I am using the asp.net default controls. How do i get the username tha ...