CS0117: 'Membership' does not contain a definition for 'GetUser'

Question

Mesmo tendo using System.Web.Security; no topo do meu arquivo, eu sempre recebo essa mensagem de erro ao compilar meu codigo: 

CS0117: 'Membership' does not contain a definition for 'GetUser'

Pq isso esta acontecendo ?

Answer 1

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Security;

public partial class Lectures: System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (System.Web.Security.Membership.GetUser() != null)
        {
            System.Web.Security.MembershipUser m = Membership.GetUser();

            try
            {