current.user.identity remains same even if another user logs in

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C#

C#4.0

Im trying to display items in a dropdown list according to the user id.The problem is that even though I log in with a diffrent username the previous or the very first username that i logged with is picked.I dnt know why its behaving like this.

To get the username in another web form im using
string username = HttpContext.Current.User.Identity.Name;

and username always remains of one persons name..and for the login im using:

public void btnlogin_Click(object sender, EventArgs e)
  {
      using (DirectoryEntry entry = new DirectoryEntry())
      {
          //Session["username"] = txtusername;
          entry.Username = txtusername.Text;
          entry.Password = txtpassword.Text;

          DirectorySearcher searcher = new DirectorySearcher(entry);

          searcher.Filter = "(objectclass=user)";

          try
          {
              searcher.FindOne();

              lblrem.Text = "Successfull";
              Response.Redirect("Default2.aspx");
          }
          catch (COMException ex)
          {
              if (ex.ErrorCode == -2147023570)
              {
                  lblrem.Text = "Login Failed.Please ensure that your username and password is correct";
              }
          }
      }