jquery ajax 问题

我用vs2010 写了一段ajax 可是怎么都没有反应，我调试了，执行这个ajax方法。但是后台的程序怎么都不执行。郁闷了！各位高手帮忙看看<script type="text/javascript">
                              $(document).ready(function () {
                                  $("#ImgBut").click(function () {
                                      var str;
                                      $("#sortable li").each(
                                        function () {
                                            str = str + $(this).attr('id');
                                        })
                                      Orders(str);
                                  })
                                  function Orders(con) {
                                      $.ajax({
                                          type: "post",
                                          contentType: "application/json",
                                          url: "select1.aspx/Orders",
                                          data: "{con:" + con + "}",
                                          datatype: "json",
                                          success: function (data) {
                                              if (data.d=="true") {
                                                  alert("正确！");
                                                  window.location.href = "/choose/select2.aspx"
                                              }
                                              else {
                                                  alert("排序错误！");
                                              }
                                          }
                                      })
                                  }
                              })
                          </script>
[WebMethod]
    public static string Orders(string con)
    {
        string strcon = "undefinedli1li2li3li4li5li6li7li8li9li10li11li12li13li14";
        if (strcon == con)
        {
            return "true";
        }
        else
        {
            return "false";
        }
    }
                        <td colspan="2" align="center" height="30px">
                           <img alt="单击提交" src="/images/tjwt.jpg" id="ImgBut" />
                        </td>