function callback() {
            if (xmlHttp.readyState == 4) {
                if (xmlHttp.status == 200) {
                  
                    var mes = xmlHttp.responseXML.getElementsByTagName("message")[0]; 
                    alert(mes);
                    var val = xmlHttp.responseXML.getElementsByTagName("passed")[0].Text;//
                    setMessage(mes, val);
                    alert("b");
                     
                }
            }
        }

context.Response.Write("<?xml version=\"1.0\"?><response><passed>False</passed><message>You have entered an invalid date.</message></response>");