map.setUIToDefault(); error

Question

below code is working fine in fire fox and google chromo but in Internet explore 9 is not working. its getting error in "map.setUIToDefault();"

var map = null;
    var geocoder = null;
    if (GBrowserIsCompatible()) {
    var map = new GMap2(document.getElementById('map_canvas_big'));
        map.setUIToDefault();
        map.disableScrollWheelZoom();
    var markerBounds = new GLatLngBounds(); 

How 2 solve this?