Delete User who is logged In

If a user who is logged in wants to delete his own account, why does login status still show him loggedIn even when user has been actually deleted.
What I want is when user deletes his account he should get logged out also at the same time ....
How do i log him out ?



If User.Identity.Name = LstBoxUserList.SelectedItem.Text Then
FormsAuthentication.SignOut()
Call deleteSelectedUser()
End If


User is deleted successfully by the above code , but login status still shows him logged  in also gives an exception

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:


Line 25: Call deleteSelectedUser()
Line 26:
Line 27: ...