เขียน code .net ด้วย c# แล้วมัน error ค่ะ วานผู้รู้ช่วยตอบด้วยค่ะ

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Xml.Linq;

namespace WebService1
{
    /// <summary>
    /// Summary description for Service1
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    [ToolboxItem(false)]
    // To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line. 
    // [System.Web.Script.Services.ScriptService]
    public class Service1 : System.Web.Services.WebService
    {

        [WebMethod]
        public string HelloWorld()
        {
            DataSet ds = new DataSet("customers");
            DataTable dt = new DataTable("customer");
            ds.Tables.Add(dt);

            DataColumn dc1 = new DataColumn("ids", typeof(int));
            dt.Columns.Add(dc1);

            DataColumn dc2 = new DataColumn("name", typeof(string));
            dt.Columns.Add(dc2);

            DataColumn dc3 = new DataColumn("surname", typeof(string));
            dt.Columns.Add(dc3);

            DataColumn dc4 = new DataColumn("address", typeof(string));
            dt.Columns.Add(dc4);

         
            DataRow dr1 = dt.NewRow();
            dr1["ids"] = 5;
            dr1["name"] = "kumaree";
            dr1["surname"] = "yanprapas";
            dr1["address"] = "sss";

            DataRow dr2 = dt.NewRow();
            dr2["ids"] = 5;
            dr2["name"] = "k";
            dr2["surname"] = "y";
            dr2["address"] = "sss";

            DataRow dr3 = dt.NewRow();
            dr3["ids"] = 5;
            dr3["name"] = "o";
            dr2["surname"] = "p";
            dr3["address"] = "sss";
            dt.Rows.Add(dr1);
            dt.Rows.Add(dr2);
            dt.Rows.Add(dr3);

            string strFullname = "";
            DataRow[] arraydr = dt.Select("ids=" + Int32.Parse(ids));  ***

            //DataRow Modifydr = 

            //dt.WriteXml("c:\\ITE499.xml");
            return "Hello World";
        }
    }
}