求教jquery调用不到后台方法？

后台代码：
using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.Services;
public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    [WebMethod]
    public static string SayHello()
    {
        return "OK!!!!!!!!";
    }
}

前台代码：
<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
  <script type="text/javascript" src="Scripts/jquery-1.6.2-vsdoc.js"></script>
  <script type="text/javascript">
$(function() {
    $("#btnOK").click(function() {
        $.ajax({
            type: "Post",
            url: "Default.aspx/SayHello",
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: function(data) {
                alert(data.d);
            },
            error: function(err) {
                alert('错误');
            }
        });

        return false;
    });
});

</script>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <input id="btnOK" type="button" value="click me" />

    </div>
    </form>
</body>
</html>

调用不到后台方法，请问什么原因？？ --------------------编程问答-------------------- 请求地址正确吗 --------------------编程问答-------------------- <script type="text/javascript" src="Scripts/jquery-1.6.2-vsdoc.js"></script> 这里引用错了，引用jquery <script src="Scripts/jquery-1.6.2.min.js" type="text/javascript"></script> --------------------编程问答-------------------- 换成4.0可以调用到。2.0调用不到。请问2.0要怎么样才能调用到？ --------------------编程问答--------------------

补充：.NET技术 ,  ASP.NET