Ошибка при подключении файла к обработчику ajax

<script language="javascript">
function XmlHttp()
{
var xmlhttp;
try{xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");}
catch(e)
{
 try {xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");} 
 catch (E) {xmlhttp = false;}
}
if (!xmlhttp && typeof XMLHttpRequest!='undefined')
{
 xmlhttp = new XMLHttpRequest();
}
  return xmlhttp;
}
 
function ajax(param)
{
                if (window.XMLHttpRequest) req = new XmlHttp();
                method=(!param.method ? "POST" : param.method.toUpperCase());
 
                if(method=="GET")
                {
                               send=null;
                               param.url=param.url+"&ajax=true";
                }
                else
                {
                               send="";
                               for (var i in param.data) send+= i+"="+param.data[i]+"&";
                               send=send;
                }
 
                req.open(method, param.url, true);
                if(param.statbox)document.getElementById(param.statbox).innerHTML = '<img src="wait.gif">';
                req.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
                req.send(send);
                req.onreadystatechange = function()
                {
                               if (req.readyState == 4 && req.status == 200) //если ответ положительный
                               {
                                               if(param.success)param.success(req.responseText);
                               }
                }
}
</script>
<div id="status">

</div>
                <form action="engine/modules/test_ajax.php">
                <p><b>На сколько увеличить</b></p>
                <p><input id="area_1" value="1" /></p>
                <input type='button' value='TEST AJAX' onclick='
                               ajax({
                                                               url:"engine/modules/test_ajax.php",
                                                               statbox:"status",
                                                               method:"POST",
                                                               data:
                                                               {
                                                                              first_area:document.getElementById("area_1").value,
                                                                              
                                                              },
                                                               success:function(data){document.getElementById("status").innerHTML=data;}
                                               })'
                >
                </form>

<?php 


header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);
sleep(2);
while(list ($key, $val) = each ($_POST))
{
                $val = iconv("UTF-8","CP1251", $_POST[$key]);
                echo "<b>Предупреждение выдано</b>";
}

?>