为什么页面不能在指定的框架内显示。(treeview)

框架页：  
<html>  
           <head>  
                       <META  HTTP-EQUIV="Content-Type"  CONTENT="text/html;  charset=gb2312">  
                       <title>内容框架集</title>  
                       <meta  name="GENERATOR"  content="Microsoft  Visual  Studio  .NET  7.1">  
                       <meta  content="http://schemas.microsoft.com/intellisense/ie5"  name="vs_targetSchema">  
           </head>  
           <FRAMESET  rows="*,0">  
                       <FRAMESET  frameSpacing="4"  frameBorder="1"  cols="200,*">  
                                   <FRAME  name="contents"  src="webmenu/framenu.aspx"  scrolling="no">  
                                   <FRAMESET  frameBorder="0"  cols="220,*">  
                                               <FRAME  name="detail"  src="detail/middlefram.aspx"  scrolling="no">  
                                               <FRAME  src=""  noResize  scrolling="no"  name="mainframe">  
                                   </FRAMESET>  
                       </FRAMESET>  
                       <FRAME  src="state/state.aspx">  
           </FRAMESET>  
</html>  
framenu.aspx(导航树）  
<html>  
<form  id="Form2"  method="post"  runat="server">  
                                   <iewc:TreeView  id="tvMenu"  style="Z-INDEX:  101;  LEFT:  8px;  POSITION:  absolute;  TOP:  25px"  runat="server"  target="mainframe">  
                                   </iewc:TreeView>  
                       </form>  
           </BODY>  
</html> 
framenu.aspx.cs(部分） 
foreach(DataRowView  drv  in  dv)  
                                   {  
                                               tmpNd  =  new  TreeNode();  
                                               tmpNd.ID  =  drv["NodeId"].ToString();  
                                               tmpNd.Text  =  drv["NodeName"].ToString();  
                                               tmpNd.ImageUrl  =  "images/"+drv["Icon"].ToString();  
                                               tmpNd.SelectedImageUrl  ="images/"+drv["selected"].ToString();  
                                               tmpNd.ExpandedImageUrl  =  "images/"+drv["expanded"].ToString();  
                                               tmpNd.NavigateUrl  =  drv["location"].ToString();  
                                               tmpNd.Expanded=True;  
                                               tmpNd.Target="mainframe";  
                                               Nds.Add(tmpNd);  
                                               intId  =  drv["ParentId"].ToString();  
                                               InitTree(tmpNd.Nodes,tmpNd.ID);                                      
                                   }  
                       }
为什么这些项不起作用：tmpNd.ExpandedImageUrl  tmpNd.Target="mainframe";  tmpNd.SelectedImageUrl  多谢了！！1