Acess denied error in asp.net

<?xml version="1.0" encoding="utf-8"?>
<newsInfo>
  <news>
    <id>1</id>
    <title>AGM (Annual General Meeting) was held on 16th June (Saturday), New Executive Committee has taken charge.</title>
    <link>../contact.aspx</link>
  </news>
  <news>
    <id>2</id>
    <title>IETE Surat  center is thinking to hold its first examination center at SURAT in December 2012, For more Information please  send your feedback here.</title>
    <link>../contact.aspx</link>
  </news>
</newsInfo>

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            if (Session["7856_UserID"] == null)
            {
                Response.Redirect("Default.aspx");

            }
            else
            {
                lblUserName.Text = "Welcome " + Convert.ToString(Session["7856_UserID"]) + "!";
                fillgrid();
            }
        }
    }
    protected DataTable retriveDetailsFromXML()
    {
        XDocument xmlDoc = XDocument.Load(Server.MapPath("~\\Data\\newsInfo.xml"));
        var com = from committee in xmlDoc.Descendants("news")
                  select new
                  {
                      id = committee.Element("id").Value,
                      title = committee.Element("title").Value,
                      link = committee.Element("link").Value,
                  };
        DataTable dt = getTable();
        foreach (var c in com)
        {
            DataRow dr = dt.NewRow();
            dr["id"] = c.id;
            dr["title"] = c.title;
            dr["link"] = c.link;
            dt.Rows.Add(dr);
        }
        return dt;
    }
    protected DataTable getTable()
    {
        DataTable dt = new DataTable();
        dt.Columns.Add("id");
        dt.Columns.Add("title");
        dt.Columns.Add("link");
        return dt;
    }
    protected void fillgrid()
    {

        ASPxGridView1.DataSource = retriveDetailsFromXML();
        ASPxGridView1.DataBind();
    }
    protected void btnAddNew_Click(object sender, EventArgs e)
    {
        ASPxGridView1.AddNewRow();
    }
    protected void ASPxGridView1_RowInserting(object sender, DevExpress.Web.Data.ASPxDataInsertingEventArgs e)
    {
            DataTable dt = retriveDetailsFromXML();
            XDocument doc = XDocument.Load(Server.MapPath("~\\Data\\newsInfo.xml"));
            doc.Element("newsInfo").Add(new XElement("news", new XElement("id", Convert.ToInt32(dt.Rows[dt.Rows.Count - 1][0]) + 1), new XElement("title", e.NewValues[0]), new XElement("link", e.NewValues[1])));
            doc.Save(Server.MapPath("~\\Data\\newsInfo.xml"));
            fillgrid();
        
        ASPxGridView1.CancelEdit();
        e.Cancel = true;

    }
    protected void ASPxGridView1_RowUpdating(object sender, DevExpress.Web.Data.ASPxDataUpdatingEventArgs e)
    {

        if (Session["KeyValue"] != null)
        {
            Int32 key = Convert.ToInt32(Session["KeyValue"]);
            XDocument doc = XDocument.Load(Server.MapPath("~\\Data\\newsInfo.xml"));
            IEnumerable<XElement> com = doc.Elements("newsInfo").Elements("news");
            var oCom = (from member in com
                        where member.Element("id").Value == key.ToString()
                        select member).SingleOrDefault();
            oCom.SetElementValue("title", e.NewValues[0]);
            oCom.SetElementValue("link", e.NewValues[1]);
           
            doc.Save(Server.MapPath("~\\Data\\newsInfo.xml"));
            Session["KeyValue"] = null;
        }
        fillgrid();


        ASPxGridView1.CancelEdit();
        e.Cancel = true;

    }
    protected void ASPxGridView1_StartRowEditing(object sender, DevExpress.Web.Data.ASPxStartRowEditingEventArgs e)
    {
        Session["KeyValue"] = Convert.ToInt32(ASPxGridView1.GetRowValuesByKeyValue(e.EditingKeyValue, "id"));
    }
    protected void ASPxGridView1_RowDeleting(object sender, DevExpress.Web.Data.ASPxDataDeletingEventArgs e)
    {
        XDocument doc = XDocument.Load(Server.MapPath("~\\Data\\newsInfo.xml"));
        doc.Element("newsInfo").Elements("news").Where(x => x.Element("id").Value.Trim() == e.Keys["id"].ToString()).Remove();
        doc.Save(Server.MapPath("~\\Data\\newsInfo.xml"));
        fillgrid();

        e.Cancel = true;
    }