نحوه ساخت RSS Feed

مطلب خیلی خوبی بود اما در قسمت sqlconnection  به مشکل بر خورد کردم چون وقتی کد رو اجرا می کنم خطا می گیره و می گه:

object reference not set to an instance of an object asp.net

و با وجود اینکه کد رو تغییر دادم اجرا نمی شه...

ممنون می شم اگه در این زمینه هم کمکم کنید...

این کد cs من هستش:

db_MyExampleDbEntities context=new db_MyExampleDbEntities();
        protected void Page_Load(object sender, EventArgs e)
        {
            //Response.Clear();
            //Response.ContentType = "application/rss+xml";
            //XmlTextWriter objX = new XmlTextWriter(Response.OutputStream, Encoding.UTF8);
            //objX.WriteStartDocument();
            //objX.WriteStartElement("rss");
            //objX.WriteAttributeString("version", "2.0");
            //objX.WriteStartElement("channel");

            ////SqlCommand cmd = new SqlCommand("Select TOP 10 * From News ORDER BY ID DESC", new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString));
            ////cmd.Connection.Open();
            ////SqlDataReader dr = cmd.ExecuteReader();

            //objX.WriteElementString("title", "SuicidePrevention.care Rss Feed");
            //objX.WriteElementString("link", "http://SuicidePrevention.care/");
            //objX.WriteElementString("description", "");
            //objX.WriteElementString("language", "en-us");
            //objX.WriteElementString("ttl", "60");
            //objX.WriteElementString("image", "");
            //objX.WriteElementString("lastBuildDate", String.Format("{0:R}", DateTime.Now));

            //var b = (from c in context.News where c.IsActive == true  select c).ToList();

            //foreach (var newse in b)
            //{
            //    int txt = newse.NewsID;
            //    var g = (from c in context.News_Group_Connections
            //             where c.NewsID == txt
            //             join r in context.News_Group on c.NewsGroupID equals r.NewsGroupID
            //             select r.NewsGroupTitle).First();
                 
            //    objX.WriteStartElement("item");
            //    objX.WriteElementString("title", newse.NewsTitle);
            //    objX.WriteElementString("author", "VBasic.net");
            //    objX.WriteElementString("link", newse.NewsLinkAddress);
            //    objX.WriteStartElement("guid");
            //    objX.WriteAttributeString("isPermaLink", "true");
            //    objX.WriteString("http://SuicidePrevention.care/");
            //    objX.WriteEndElement();
            //    //objX.WriteElementString("pubDate", DateTime.Parse(newse.NewsDate.ToString()).ToString("MM/dd/yyyy"));
            //    objX.WriteElementString("pubDate", String.Format("{0:R}", newse.NewsDate));
            //    objX.WriteStartElement("category");
            //    objX.WriteString(g);
            //    objX.WriteEndElement();
            //    objX.WriteElementString("description", newse.NewsDescription);
            //    objX.WriteEndElement();
            //}
            ////while (dr.Read())
            ////{
            ////    objX.WriteStartElement("NewsTitle");
                
            ////    objX.WriteEndElement();
            ////    objX.WriteElementString("description", dr["Article"].ToString().Substring(0, 100) + "..");
            ////    objX.WriteEndElement();
            ////}

            //objX.WriteEndElement();
            //objX.WriteEndElement();
            //objX.WriteEndDocument();
            //objX.Flush();
            //objX.Close();
            //Response.End();
            Response.Clear();
            Response.ContentType = "application/rss+xml";
            XmlTextWriter objX = new XmlTextWriter(Response.OutputStream, Encoding.UTF8);
            objX.WriteStartDocument();
            objX.WriteStartElement("rss");
            objX.WriteAttributeString("version", "2.0");
            objX.WriteStartElement("channel");
            SqlCommand cmd = new SqlCommand("Select TOP 10 * From News ORDER BY ID DESC", new SqlConnection(ConfigurationManager.ConnectionStrings["Server=.;User ID=sa; Database=db_MyExampleDb; Password=Mypass"].ConnectionString));
            cmd.Connection.Open();
            SqlDataReader dr = cmd.ExecuteReader();
            objX.WriteElementString("title", "مرجع تخصصی برنامه نویسی | آموزش برنامه نویسی");
            objX.WriteElementString("link", "http://www.madaeny.com/");
            objX.WriteElementString("description", "آموزش برنامه نویسی و مقالات برنامه نویسی نمونه کد های سی شارپ آموزش برنامه نویسی در آموزشگاه برنامه نویس");
            objX.WriteElementString("language", "fa-ir");
            objX.WriteElementString("ttl", "60");
            objX.WriteElementString("image", "http://www.madaeny.com/SiteImages/logo.png");
            objX.WriteElementString("lastBuildDate", String.Format("{0:R}", DateTime.Now));
            while (dr.Read())
            {
                objX.WriteStartElement("item");
                objX.WriteElementString("title", dr["NewsTitle"].ToString());
                objX.WriteElementString("author", "C# .net");
                objX.WriteElementString("link", "http://www.madaeny.com/");
                objX.WriteStartElement("guid");
                objX.WriteAttributeString("isPermaLink", "true");
                objX.WriteString("http://www.madaeny.com/");
                objX.WriteEndElement();
                objX.WriteElementString("pubDate", String.Format("{0:R}", dr["NewsDate"]));
                objX.WriteStartElement("category");
                objX.WriteString(dr["Category"].ToString());
                objX.WriteEndElement();
                objX.WriteElementString("description", dr["NewsDescription"].ToString());
                objX.WriteEndElement();
            }
            objX.WriteEndElement();
            objX.WriteEndElement();
            objX.WriteEndDocument();
            objX.Flush();
            objX.Close();
            Response.End();