Ext.onReady(function() {
    //树的节点
         var root = new Ext.tree.AsyncTreeNode({
             id: "root",
             text: "根目录",         
             draggable:false,
             expanded: true //展开            
         });
   var tree=new Ext.tree.TreePanel({
   title:"Extjs动态树",
   width:600,
   autoScroll:true,    
      animate:true,    
      enableDD:true,  
      root:root,  
      containerScroll: true,
   loader:new Ext.tree.TreeLoader({
      dataUrl:'BusinessCode!Business.action'
      })
     
   
   });
    tree.setRootNode(root);
    tree.render("tree");
});
json 数据没问题。
[{"id":10,"text":"Benz","leaf":false,"cls":"folder","children":[{"id":11,"text":"S600","leaf":true,"cls":"file"},{"id":12,"text":"SLK200","leaf":true,"cls":"file"}]},{"id":20,"text":"BMW","leaf":false,"cls":"folder","children":[{"id":21,"text":"325i","leaf":true,"cls":"file"},{"id":22,"text":"X5","leaf":true,"cls":"file"}]}]       


我也遇到类似这样的问题，好像是在节点reload的时候报出来的，郁闷