调错

以下代码报错：错误：长度不能小于 0。 
              参数名: length 
哪里错了啊？ 
using System; 
using System.Collections.Generic; 
using System.ComponentModel; 
using System.Data; 
using System.Drawing; 
using System.Text; 
using System.Windows.Forms; 
using System.Net; 
using System.IO; 
using System.Data.SqlClient; 
using System.Text.RegularExpressions; namespace WindowsApplication2 
{ 
    public partial class Form1 : Form 
    { 
        public Form1() 
        { 
            InitializeComponent(); 
        }         private void button1_Click(object sender, EventArgs e) 
        { 
            string strResult = ""; 
            try 
            { 
                string Url = "http://list.mp3.baidu.com/topso/mp3topsong.html?id=1#top2";                 HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url); 
                //声明一个HttpWebRequest请求 
                request.Timeout = 30000; 
                //设置连接超时时间 
                request.Headers.Set("Pragma", "no-cache"); 
                HttpWebResponse response = (HttpWebResponse)request.GetResponse(); 
                Stream streamReceive = response.GetResponseStream(); 
                Encoding encoding = Encoding.GetEncoding("GB2312"); 
                StreamReader streamReader = new StreamReader(streamReceive, encoding); 
                strResult = streamReader.ReadToEnd(); 
                //取出和数据有关的那段源码 
                int iBodyStart = strResult.IndexOf(" <body", 0); 
                int iStart = strResult.IndexOf("歌曲TOP500", iBodyStart); 
                int iTableStart = strResult.IndexOf(" <table", iStart); 
                int iTableEnd = strResult.IndexOf(" </table>", iTableStart); 
                string strWeb = strResult.Substring(iTableStart, iTableEnd - iTableStart + 8);                 //生成HtmlDocument 
                WebBrowser webb = new WebBrowser(); 
                webb.Navigate("about:blank"); 
                HtmlDocument htmldoc = webb.Document.OpenNew(true); 
                htmldoc.Write(strWeb); 
                HtmlElementCollection htmlTR = htmldoc.GetElementsByTagName("TR"); 
                foreach (HtmlElement tr in htmlTR) 
                { 
                    string strID = tr.GetElementsByTagName("TD")[0].InnerText; 
                    Console.WriteLine(tr.GetElementsByTagName("TD")[1].InnerText); 
                    string strName = SplitName(tr.GetElementsByTagName("TD")[1].InnerText, "MusicName"); 
                    string strSinger = SplitName(tr.GetElementsByTagName("TD")[1].InnerText, "Singer"); 
                    strID = strID.Replace(".", ""); 
                    //插入DataTable 
                    //AddLine(strID, strName, strSinger, "0");                     string strID1 = tr.GetElementsByTagName("TD")[2].InnerText; 
                    Console.WriteLine(tr.GetElementsByTagName("TD")[3].InnerText); 
                    string strName1 = SplitName(tr.GetElementsByTagName("TD")[3].InnerText, "MusicName"); 
                    string strSinger1 = SplitName(tr.GetElementsByTagName("TD")[3].InnerText, "Singer"); 
                    //插入DataTable 
                    strID1 = strID1.Replace(".", ""); 
                  //AddLine(strID1, strName1, strSinger1, "0");                     string strID2 = tr.GetElementsByTagName("TD")[4].InnerText; 
                    Console.WriteLine(tr.GetElementsByTagName("TD")[5].InnerText); 
                    string strName2 = SplitName(tr.GetElementsByTagName("TD")[5].InnerText, "MusicName"); 
                    string strSinger2 = SplitName(tr.GetElementsByTagName("TD")[5].InnerText, "Singer"); 
                    //插入DataTable 
                    strID2 = strID2.Replace(".", ""); 
                    //AddLine(strID2, strName2, strSinger2, "0");                 } 
            } 
            catch (Exception exp) 
            { 
                strResult = "错误：" + exp.Message; 
            } 
            this.richTextBox1.Text = strResult;         }         public string SplitName(string longStrName, string name) 
        { 
            string result = ""; 
            if (name.Equals("MusicName")) 
            { 
                result = longStrName.Substring(0, longStrName.IndexOf("(") - 1); 
                Console.WriteLine(result);             } 
            else if (name.Equals("Singer")) 
            { 
                result = longStrName.Substring(longStrName.IndexOf("(") + 1).TrimEnd(new char[] { ')' }); 
                Console.WriteLine(result);             } 
            return result; 
        }           } 
}