急需解决，ArcGIS Server JavaScript的问题

Question

提示：tileInfo.lods为空或不是对象？
    我不知道为什么。
  <script type="text/javascript" language="Javascript" src="http://localhost:8888/JQGIS/jsapi/js/dojo/dojo/dojo.js">
    </script>
    <script type="text/javascript" language="Javascript" src="http://localhost:8888/JQGIS/jsapi/arcgis.js">
    </script>
<script type="text/javascript">
dojo.require("esri.map"); var map;

var mapURL = "http://192.168.0.134:8399/arcgis/rest/services/Usa/MapServer";
function init() {
map = new esri.Map("map");
var layer = new esri.layers.ArcGISTiledMapServiceLayer(mapURL, {id:"usa"});
if(layer.loaded){
initMap(layer);
}else{
                    dojo.connect(layer,"onLoad",initMap);
}    

}

function initMap(layer){
            var labels=[];
var lods=layer.tileInfo.lods;
for(var i=0;i<lods.length;i++){
labels[i]=lods[i].scale;
}

       esriConfig.defaults.map.slider = { right:"10px", bottom:"10px", width:"200px", height:null };
esriConfig.defaults.map.sliderLabel={
               tick:2,
               labels:labels,
               style:"width:2em;font-family:Verdana;font-size:65%;color:#fff;padding-left:2px;"
              };
             map.addLayer(layer);  
        
} dojo.addOnLoad(init);
</script>