MooTools Submit stop event

[shile]

well,i have this script that i have set up that on submit requests php file that is used to validate my input values...i have set up that when it is not validated the correct way to echo it is not validated,now i want in my request when i get response and it is the error response to stop the submit..here is the script,it does send the request and returns response but it doesnt stop the submit...

window.addEvent('domready', function(){
var form=document.adminForm;
form.addEvent('submit', function(e){


    var dataString="date=" + document.getElementById("date").value + "&start=" + document.getElementById("start").value + "&end=" + document.getElementById("end").value;
    var requestData = new Request ({
                url: '/provjera.php',
                method:'POST',
            async:false,
             evalResponse:true,
                data:dataString,
                onComplete: function(responseText){
                 alert(responseText);
                if(responseText){}
                e.stop();

                }
            });

            requestData.send();

});


});