动态调用WebServices时出的有关问题,请帮助呀

using System;
using System.Web;
using System.Xml;
using System.Collections;
using System.Net;
using System.Text;
using System.IO;
/// <summary>
/// WebService 的摘要说明
/// </summary>
public class WebService
{
    public WebService()
    {
         //<webServices>
    //  <protocols>
    //    <add name="HttpGet"/>
    //    <add name="HttpPost"/>
    //  </protocols>
    //</webServices>
    }
    private static Hashtable _xmlNamespaces = new Hashtable();//缓存xmlNamespace，避免重复调用GetNamespace

    /**/
    /// <summary>
    /// 需要WebService支持Post调用
    /// </summary>
    public static XmlDocument QueryPostWebService(String URL, String MethodName, Hashtable Pars)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL );
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";
        SetWebRequest(request);
        byte[] data = EncodePars(Pars);
        WriteRequestData(request, data);

        return ReadXmlResponse(request.GetResponse());
    }
    /**/
    /// <summary>
    /// 需要WebService支持Get调用
    /// </summary>
    public static XmlDocument QueryGetWebService(String URL, String MethodName, Hashtable Pars)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL + "/" + MethodName + "?" + ParsToString(Pars));
        request.Method = "GET";
        request.ContentType = "application/x-www-form-urlencoded";
        SetWebRequest(request);
        return ReadXmlResponse(request.GetResponse());
    }


    /**/
    /// <summary>
    /// 通用WebService调用(Soap),参数Pars为String类型的参数名、参数值
    /// </summary>
    public static XmlDocument QuerySoapWebService(String URL, String MethodName, Hashtable Pars)
    {
        //By 同济黄正 http://hz932.ys168.com 2008-3-19
        if (_xmlNamespaces.ContainsKey(URL))
        {
            return QuerySoapWebService(URL, MethodName, Pars, _xmlNamespaces[URL].ToString());
        }
        else
        {
            return QuerySoapWebService(URL, MethodName, Pars, GetNamespace(URL));
        }
    }

    private static XmlDocument QuerySoapWebService(String URL, String MethodName, Hashtable Pars, string XmlNs)
    {
        _xmlNamespaces[URL] = XmlNs;//加入缓存，提高效率
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(URL);
        request.Method = "POST";
        request.ContentType = "text/xml; charset=utf-8";
        request.Headers.Add("SOAPAction", "" + XmlNs + (XmlNs.EndsWith("/") ? "" : "/") + MethodName + "");
        request.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)";//LSH 2011-01-10

        SetWebRequest(request);
        byte[] data = EncodeParsToSoap(Pars, XmlNs, MethodName);
        WriteRequestData(request, data);
        XmlDocument doc = new XmlDocument(), doc2 = new XmlDocument();
        doc = ReadXmlResponse(request.GetResponse());

        XmlNamespaceManager mgr = new XmlNamespaceManager(doc.NameTable);
        mgr.AddNamespace("soap", "http://schemas.xmlsoap.org/soap/envelope/");
        String RetXml = doc.SelectSingleNode("//soap:Body/*", mgr).InnerXml;
        doc2.LoadXml("<root>" + RetXml + "</root>");
        AddDelaration(doc2);
        return doc2;
    }
    private static string GetNamespace(String URL)
    {
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(URL + "?WSDL");
        SetWebRequest(request);
        WebResponse response = request.GetResponse();
        StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(sr.ReadToEnd());
        return doc.SelectSingleNode("//@targetNamespace").Value;
    }
    private static byte[] EncodeParsToSoap(Hashtable Pars, String XmlNs, String MethodName)
    {
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(@"<soap:Envelope xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"" xmlns:soap=""http://schemas.xmlsoap.org/soap/envelope/""></soap:Envelope>");
        AddDelaration(doc);
        XmlElement soapBody = doc.CreateElement("soap", "Body", "http://schemas.xmlsoap.org/soap/envelope/");
        XmlElement soapMethod = doc.CreateElement(MethodName);
        soapMethod.SetAttribute("xmlns", XmlNs);
        foreach (string k in Pars.Keys)
        {
            XmlElement soapPar = doc.CreateElement(k);
            soapPar.InnerText = Pars[k].ToString();
            soapMethod.AppendChild(soapPar);
        }
        soapBody.AppendChild(soapMethod);
        doc.DocumentElement.AppendChild(soapBody);
        return Encoding.UTF8.GetBytes(doc.OuterXml);
    }

    private static void SetWebRequest(HttpWebRequest request)
    {
        request.Credentials = CredentialCache.DefaultCredentials;
        request.Timeout = 1000000;
    }

    private static void WriteRequestData(HttpWebRequest request, byte[] data)
    {
        request.ContentLength = data.Length;
        Stream writer = request.GetRequestStream();
        writer.Write(data, 0, data.Length);
        writer.Close();
    }

    private static byte[] EncodePars(Hashtable Pars)
    {
        return Encoding.UTF8.GetBytes(ParsToString(Pars));
    }

    private static String ParsToString(Hashtable Pars)
    {
        StringBuilder sb = new StringBuilder();
        foreach (string k in Pars.Keys)
        {
            if (sb.Length > 0)
            {
                sb.Append("&");
            }
            //sb.Append(HttpUtility.UrlEncode(k) + "=" + HttpUtility.UrlEncode(Pars[k].ToString()));
            sb.Append(Pars[k].ToString());
        }
        return sb.ToString();
    }

    private static XmlDocument ReadXmlResponse(WebResponse response)
    {
        StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.UTF8);
        String retXml = sr.ReadToEnd();
        sr.Close();
        XmlDocument doc = new XmlDocument();
        doc.LoadXml(retXml);
        return doc;
    }

    private static void AddDelaration(XmlDocument doc)
    {
        XmlDeclaration decl = doc.CreateXmlDeclaration("1.0", "utf-8", null);
        doc.InsertBefore(decl, doc.DocumentElement);
    }
    
}