why geting null-result from OpenLSLUS_Geocode.php?

Hello,

I try to use part of the example http://openlayers.org/dev/examples/openls.html to include a map in my website and let users search for the address. But I alway get a null-value as response.responseXML.

To verify that I have no error in my code I have copied the whole example to my site. Calling it shows the same error as the code in my own site (for the example see code below).

I found a posting in an OSM-forum that I have to use a proxy and so I have installed proxy.php from the mapbuilder-site and changed the code like follows:

            function init() {
            OpenLayers.ProxyHost = "proxy.php?url=";
            map = new OpenLayers.Map('map', {
                controls: [
                    new OpenLayers.Control.PanZoom(),
                    new OpenLayers.Control.Navigation()
                ]
            });
            layer = new OpenLayers.Layer.OSM("OpenStreetMap", null, {
                transitionEffect: 'resize'
            });
            map.addLayers([layer]);
            map.zoomToMaxExtent();
        }
        function submitform() {
           var queryString = document.forms[0].query.value;
            OpenLayers.Request.POST({
                url: "http://www.openrouteservice.org/php/OpenLSLUS_Geocode.php",
                scope: this,
                failure: this.requestFailure,
                success: this.requestSuccess,
                headers: {"Content-Type": "application/x-www-form-urlencoded"},
                data: "FreeFormAdress=" + encodeURIComponent(queryString) + "&MaxResponse=1"
            });
        }
        function requestSuccess(response) {
alert(response.responseXML);
            var format = new OpenLayers.Format.XLS();
            var output = format.read(response.responseXML);
            if (output.responseLists[0]) {
                var geometry = output.responseLists[0].features[0].geometry;
                var foundPosition = new OpenLayers.LonLat(geometry.x, geometry.y).transform(
                        new OpenLayers.Projection("EPSG:4326"),
                        map.getProjectionObject()
                        );
                map.setCenter(foundPosition, 16);
            } else {
                alert("Sorry, no address found");
            }
        }
        function requestFailure(response) {
            alert("An error occurred while communicating with the OpenLS service. Please try again.");
        }

The alert in function requestSuccess(response) returns null whatever I set as proxy. I have tried with "", "proxy.php", "proxy.php?url=", all with the same result. The only diffenrence ist that with "" there are about 5 seconds from calling the service until I get the result. In all other cases (using the proxy.php) the result comes in less than one second.

What is wrong in my code?

(I also tried to use proxy.cgi, but this won't work on my server - I get an 500 internal-server-error)

Thank you for all tipps!