微信公众平台api 不能接收来自普通用户的post的消息

微信公众平台api 不能接收来自普通用户的post的消息
我的代码  如下  ：请教高手指点。为什么不能接收到消息

public partial class Default : System.Web.UI.Page,IHttpHandler
{
        const string Token = "1005sunyafen";       //与那边填写的token一致  
        protected void Page_Load(object sender, EventArgs e) 
        { 
            string postStr = ""; 
            if (Request.HttpMethod.ToLower() == "post")  //post方式毕业论文 
            {
                Stream s = Request.InputStream; 
                byte[] b = new byte[s.Length]; 
                s.Read(b, 0, (int)s.Length); 
                postStr = Encoding.UTF8.GetString(b);
                if (!string.IsNullOrEmpty(postStr)) 
                { 
                    //封装请求类  
                    XmlDocument doc = new XmlDocument(); 
                    doc.LoadXml(postStr); 
                    XmlElement rootElement = doc.DocumentElement; 
 
                    XmlNode MsgType = rootElement.SelectSingleNode("MsgType"); 
 
                    RequestXML requestXML = new RequestXML(); 
                    requestXML.ToUserName = rootElement.SelectSingleNode("ToUserName").InnerText; 
                    requestXML.FromUserName = rootElement.SelectSingleNode("FromUserName").InnerText; 
                    requestXML.CreateTime = rootElement.SelectSingleNode("CreateTime").InnerText; 
                    requestXML.MsgType = MsgType.InnerText; 
 
                    if (requestXML.MsgType == "text") 
                    { 
                        requestXML.Content = rootElement.SelectSingleNode("Content").InnerText;
                        this.con.InnerText += requestXML.Content;                    } 
                    else if (requestXML.MsgType == "location") 
                    { 
                        requestXML.Location_X = rootElement.SelectSingleNode("Location_X").InnerText; 
                        requestXML.Location_Y = rootElement.SelectSingleNode("Location_Y").InnerText; 
                        requestXML.Scale = rootElement.SelectSingleNode("Scale").InnerText; 
                        requestXML.Label = rootElement.SelectSingleNode("Label").InnerText; 
                    } 
                    else if (requestXML.MsgType == "image") 
                    { 
                        requestXML.PicUrl = rootElement.SelectSingleNode("PicUrl").InnerText; 
                    } 
 
                    //回复消息  
                    ResponseMsg(requestXML); 
                } 
            } 
            else 
            { 
                Valid(); 
            } 

    }

先在这儿调试一下能不能接收到消息

 if (!string.IsNullOrEmpty(postStr)) 
                { 

就if (Request.HttpMethod.ToLower() == "post") 看看哪步能取到