The type or namespace name 'Exchange' does not exist in the namespace 'Microsoft'

This is my code, please take a look at the screen shoot attached. I added a reference to the Exchange Web Services also. Why do I get this error all the time?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Microsoft.Exchange.WebServices.Data;
using System.Net.Security;
using System.Security.Cryptography.X509Certificates;
namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {

        }
    }
}

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