openlayers 2 - GetFeature request with polygon intersecting polygons

My task is very straightforward: a user draws a polygon and queries all parcel polygons. The query string extends the URL limit. So I am posting XML to WFS. However, GeoServer always returned 0 feature, but I knew the query polygon overlapped several tax parcels. If I passed a single point, it worked fine. Did I miss anything for sending a polygon? I used the OpenLayers buildGeometry to create the polygon GML. I can't figure out what's wrong.

Please Help.

Here is my code:

var gml = new OpenLayers.Format.GML(); 
var polygonGML = gml.buildGeometry.polygon.apply(gml,[taArray[0].geometry])
console.log(polygonGML); 

var plgGMLString = (new XMLSerializer()).serializeToString(polygonGML);

var geo_req_url = proxyHost + "http://localhost:8080/geoserver/wfs"; 
var query_xml = '    + '' 
    + 'geom'
    + plgGMLString 
    + ''; 

$.post(

    geo_req_url,
    query_xml,
    function(data) {
        geoResults = data.features;
        remove_selected_features(); 
        draw_sel_features(); 
    },
    "application/json"
);

Here is the printout of plgGMLString.

-74.00567761405651,40.546826958183715 ...