Google Map ~ GDirections.load on failed, error Event

var gdir = new GDirections(map);

GEvent.addListener( gdir, "error", function() {
alert("Failed to direction, please re-type address."); } );

var start = $('#start').val();
var end = $('#end').val();

gdir.load("from:" + start + " to:" + end);


refernce
http://groups.google.com/group/google-maps-api/browse_thread/thread/69b71853ab6cf7a7