Reading data from php

I'm doing a page with a map , who can hide and show some markers on it. Those markers are in an xml archive (xml archive)and all works fine... but now, I need change that import to an php script (php script) and those markers doesn't display correctly.

This work fine:

downloadUrl("ubicaciones.xml", function(doc) {
    var xml = xmlParse(doc);
    var markers = xml.documentElement.getElementsByTagName("marker");

    for (var i = 0; i < markers.length; i++) {
      // obtener atributos de cada marcador
      var lat = parseFloat(markers[i].getAttribute("lat"));
      var lng = parseFloat(markers[i].getAttribute("lng"));
      var point = new google.maps.LatLng(lat,lng);
      var address = markers[i].getAttribute("address");
      var name = markers[i].getAttribute("name");
      var html = "<b>"+name+"<\/b><p>"+address;
      var category = markers[i].getAttribute("category");
      // create the marker
      var marker = createMarker(point,name,html,category);
    }

But this doesn't:

downloadUrl("crear.php", function(doc) {
    var xml = xmlParse(doc);
    var markers = xml.documentElement.getElementsByTagName("marker");

    for (var i = 0; i < markers.length; i++) {
      // obtener atributos de cada marcador
      var lat = parseFloat(markers[i].getAttribute("lat"));
      var lng = parseFloat(markers[i].getAttribute("lng"));
      var point = new google.maps.LatLng(lat,lng);
      var address = markers[i].getAttribute("address");
      var name = markers[i].getAttribute("name");
      var html = "<b>"+name+"<\/b><p>"+address;
      var category = markers[i].getAttribute("category");
      // create the marker
      var marker = createMarker(point,name,html,category);
    }

any help please?