xml request gets convert to text/html request and causing 500 internal server error?

i am sending a ajax request and expecting xml response but the response gets converted to text/html .It is causing 500 internal server error too.the same code is working on my localhost.

below is a small code which shows how i am sending the request

var searchUrl = '<?php bloginfo('template_url'); ?>/phpsqlsearch_genxml-new-home-page.php?address=' + address + '&postal_code=' + postal_code + '&radius=' + radius + '&suggestion=' + suggestion;
    downloadUrl(searchUrl, function(data) {
        var xml = parseXml(data);
        var markerNodes = xml.documentElement.getElementsByTagName("marker");
        var bounds = new google.maps.LatLngBounds();
        if (markerNodes.length == 0)    /////////////check empty result/////////////
        {
        var msg = jQuery("<div/>").html("aucun r&eacute;sultat trouv&eacute;").text();
        alert(msg);

        displayAllStoresOfbrands();
        }

and below is the code of the file i am hitting my ajax request

<?php header("Content-type: text/xml");

above is the code which i have placed on the top of my ajax file