为什么ajax请求失败？

I'm trying to perform some calculations using the url shown in the below code , Everytime i run the code alert() in error:functiom is being called . PLs help

$("#button").click(function(){
    $("#form1").validationEngine();
    if($('div input[type=text]').val() != "") {
        var textfield2=document.getElementById("textfield2").value;
        var textarea=document.getElementById("textarea").value;
        var dataS=$("#form1").serialize();
        $.ajax({
            type: "POST",
            url: "http://some_site/ppp.php",
            data:dataS,
            crossDomain: true,
            success: function( ){
                $("#result").empty().html("<h2>Your request has been received </h2>"); 
            },
            error: function(){                          
                alert(dataS);
            }
        });
    }
    return false;
});

I wouldn't mess around with a cross-domain POST. I've found CORS to be notoriously difficult to get working reliably in all browsers. Some browsers will send the request but ignore the result, some will not even send the request, some will work fine.

Instead, consider using either a PHP proxy on the same domain, or use GET with JSONP to send the request instead.