TreeView.getTreeNode()步骤报错object doesn't support this property or methods

         var TreeView;
         function this_ondocumentready()
         {
        TreeView = element.all(id + "_TreeFilter");
         }
         function SyncTree()
    {    
        [color=#FF0000]var treeAnd = TreeView .getTreeNode("0");[/color]        treeAnd.setAttribute("Root", "true");
        treeAnd.setAttribute("BoolType", "And");

        var xFilter = xmlTree.selectSingleNode("//Filter");
        if( null == xFilter )
        {
            xFilter = xmlTree.createElement("Filter");
            if( xmlTree.hasChildNodes )
                xmlTree.firstChild.appendChild(xFilter);
            else
                xmlTree.appendChild(xFilter);        
        }

        var xAnd = xmlTree.selectSingleNode("//Filter/And");
        if( null == xAnd )
        {
            xAnd = xmlTree.createElement("And");
            xFilter.appendChild(xAnd);        
        }
        
        SyncNode( xAnd, treeAnd);

        TreeView.selectedNodeIndex = txtSelectedNode.value;
    }