dojo动态树加到frames总是报js错误【function "treeNodeSelected" does not exist on "[object]"】

浏览器：IE8， IE6
Tomcat 5.5
struts2.1.6

我根据网上的例子写了一个动态Ajax树，这棵树放在leftFrame里。点一个树上的节点时，会刷新rightFrame显示相应的东西。 每次重新启动tomcat然后访问页面的时候，树节点的展开/收起都没有问题，但是点击某个节点以后，再点击一个节点就会报js错：
消息: function "treeNodeSelected" does not exist on "[object]"
行: 96
字符: 1
代码: 0
URI: http://localhost:8080/portal/struts/dojo/struts_dojo.js

frame结构如下：

<frameset id="outframe" name="outframe" rows="88,0,*" cols="*" framespacing="0" frameborder="0" border="0" >	

	<frame src="top.do" name="topframe" scrolling="no"  id="topframe" TOPMARGIN="1" MARGINHEIGHT="1"/>

	<frameset id="allframe" name="allframe" rows="*" cols="18%,6,*" framespacing="0" frameborder="0" border="0" >

		 <frame src="<left.do/>" name="listframe" scrolling="auto"  id="listframe" />

	 	 <frame src="mid.jsp" name="leftBarFrame" scrolling="no"  id="leftBarFrame" noresize="noresize" LEFTMARGIN="0" MARGINWIDTH="0" />

	   	 <frame src="right.do" name="showframe" scrolling="auto" resize="no" id="showframe"/>

	</frameset>

	<frame src="HomePage.do" name="homeframe" scrolling="no"  id="homeframe" TOPMARGIN="1" MARGINHEIGHT="1"/>

</frameset>

其中listframe显示树，showframe显示点击数节点后要显示的内容。

页面的代码如下（userTree.jsp）:

<%@ page language="java" import="java.util.*" pageEncoding="GB2312"%>

<%@ taglib prefix="s" uri="/struts-tags"%>

<%@ taglib prefix="dojo" uri="/struts-dojo-tags"%>

<%

	response.setHeader("Cache-Control", "no-cache");

	response.setHeader("Cache-Control", "no-store");

	response.setDateHeader("Expires", 0);

	response.setHeader("Pragma", "no-cache");

%>

<%@ include file="/include/check.jsp"%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>

<head>



<title></title>

<meta http-equiv="pragma" content="no-cache">

<meta http-equiv="cache-control" content="no-cache">

<meta http-equiv="expires" content="0">

<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">

<meta http-equiv="description" content="This is my page">

</head>

<dojo:head />

<script type="text/javascript">

	dojo.require("dojo.lang.*");

	dojo.require("dojo.widget.*");

	dojo.require("dojo.widget.Tree");

	dojo.require("dojo.widget.TreeRPCController");

</script>

<style type="text/css">

a:visited{

	color:#12035C;

}

a:link{

	color:#12035C;

}

</style>

<script type="text/javascript">

	function treeNodeSelected(arg) {

	    if(""+arg.source.widgetId!="undefined"){

			 var url = "user/showMember.do?id=" + arg.source.widgetId;

			 top.showframe.location = url; //这句去掉就不报错了

			 alert("widgetId: "+arg.source.widgetId);

			 

	    }

	}

	

	dojo.addOnLoad(function() {

	    var t = dojo.widget.byId('memberAndUsers');

	    var s = t.selector;

	    dojo.event.connect(s, 'select', 'treeNodeSelected');

	});

	

	function refresh()

	{

		location.reload();

	}

</script>

<body bgcolor="white">

<dojo:div

	cssStyle="position:absolute; border: 0px solid black; background-color:white;">



	<a href="#"><img border="0" width="25" height="25" src="images/refresh.png" onclick="refresh()" alt="刷新" title="刷新"/></a>

	<div dojoType="TreeRPCController" widgetId="treeController"

		DNDcontroller="create" RPCUrl="<s:url />"></div>

	<div dojoType="Tree" widgetId="memberAndUsers" toggle="fade"

		controller="treeController">

	<div dojoType="TreeNode" title="<s:property value='root.title' />"

		widgetId='<s:property value="root.id" />'

		isFolder='<s:property value="root.children.length > 0" />'

		objectId='<s:property value="root.id" />'></div>

	</div>

</dojo:div>

</body>

</html>