how to retrieve contacts from gmail in asp.net

i am using code blow but there is an error : - Additional information: Execution of authentication request returned unexpected result: 404

Here Is The Code

public DataSet GetGmailContacts(string App_Name, string Uname, string UPassword)

{

DataSet ds = new DataSet();

DataTable dt = new DataTable();

dt.Columns.Add(new DataColumn("EmailID", typeof(string)));

dt.Columns.Add(new DataColumn("Name", typeof(string)));

RequestSettings rs = new RequestSettings(App_Name, Uname, UPassword);

rs.AutoPaging = true;

ContactsRequest cr = new ContactsRequest(rs);

Feed f = cr.GetContacts();

foreach (Contact t in f.Entries)

{

foreach (EMail email in t.Emails)

{

DataRow dr = dt.NewRow();

dr["EmailID"] = email.Address.ToString();

dr["Name"] = t.Title.ToString();

dt.Rows.Add(dr);

}

ds.Tables.Add(dt);

return ds;

}

protected void Page_Load(object sender, EventArgs e)

{

}

protected void btnLogin_Click(object sender, EventArgs e)

{

DataSet ds = GetGmailContacts("Gmail Contact Operations", txtName.Text, txtPwd.Text);

ViewState["Contact"] = ds;

gvContacts.DataSource = ds;

gvContacts.DataBind();

}

protected void gvContacts_PageIndexChanging(object sender, GridViewPageEventArgs e)

{

DataSet ds = ViewState["Contact"] as DataSet;

gvContacts.PageIndex = e.NewPageIndex;

gvContacts.DataSource = ds;

gvContacts.DataBind();

}