Ext.Net TreePanel rootVisible = false RequestFailure错误

Question

我有一个treepanel，我可以成功地将数据加载到treeopanel。但是 我想将treepanel的rootVisible属性设置为false。当我将rootVisible属性设置为false时，我收到类似Request Failure的错误。相关的截图如下。尽管出现错误，但它仍能正常工作。

如何克服这一点。

相关代码块是;

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        ConcreteDepartmentDefinition [] l = Department.GetDepartmentList();

        foreach (var obj in l)
        {
            if (obj.DepartmentParentOid == null || obj.DepartmentParentOid == 0)
            {
                Node root = new Node();
                root.NodeID = obj.Oid.ToString();
                root.Text = "<b>"+obj.DepartmentCode+"</b> - "+obj.DepartmentName;
                root.Icon = Icon.UserHome;
                root.Leaf = obj.IsLeaf;
                treePanel1.Root.Add(root);
                treePanel1.RootVisible = false;
            }
            else
            {
                Node newNode = new Node();
                newNode.NodeID = obj.Oid.ToString();
                newNode.Text = "<b>"+obj.DepartmentCode+"</b> - "+obj.DepartmentName;
                newNode.Icon = Icon.UserGreen;
                newNode.Leaf = obj.IsLeaf;
                treePanel1.GetNodeById(obj.DepartmentParentOid.ToString()).AppendChild(newNode);
            }
        }
    }

treepanel

treepanel2