Kendo UI Validation for Dublicate Value Checking

I am faced a problem with validation for duplicate value checking from server using json. My code is runing fine in each click but error message show in second click(One click in side text box put value then click out side the text box - that time code execute but error message show . again i click in that text box and again click out side text box ,again my code run and this time error message show) . Please find my mistake and help me to show validation message in single escape or single click of text box.

Now I solve by adding ajax async clode in the to  of the javascript. We get success if you use this.

script language="javascript" type="text/javascript"

//KendoUi Validation

    var validatable = $("#ApplicationNo").kendoValidator({
        onfocusout: true,
        onkeyup: true,
        rules: {
            ApplicationNo: function (input) {
                $.post("/Home/CheckAppNo", 

               { ApplicationNo: $("#ApplicationNo").val() }, 

               function (data) { b1 = data; })
                return b1;
              }

        },

        messages: {
            ApplicationNo: "Already Exist"
        }
    }).data("kendoValidator");

   var validatable = 

       $(".k-content").kendoValidator().data("kendoValidator");

script language="javascript" type="text/javascript" //KendoUi Validation         $.ajaxSetup({ async: false });     var validatable = $("#ApplicationNo").kendoValidator({ onfocusout: true, onkeyup: true, rules: { ApplicationNo: function (input) { $.post("/Home/CheckAppNo",    { ApplicationNo: $("#ApplicationNo").val() },  function (data) { b1 = data; }) return b1; } }, messages: { ApplicationNo: "Already Exist" } }).data("kendoValidator"); var validatable =  $(".k-content").kendoValidator().data("kendoValidator"); C # Code public JsonResult CheckAppNo(string ApplicationNo) { bool IsOk = projectRepository.CheckAppNumber(ApplicationNo); return Json(IsOk, JsonRequestBehavior.AllowGet); //return new JsonResult { Data = IsOk }; }     Html < input type="text" id="ReferredBy" name="ReferredBy" class="k-textbox" required />