AsyncFileUpload IE8不兼容？

 代码部分：     
 <asp:ScriptManager ID="scriptmanager1" runat="server"></asp:ScriptManager>   
      <asp:AsyncFileUpload ID="fu_teacher" runat="server" Width="250px" OnUploadedComplete="fu_teacher_UploadedComplete" OnClientUploadStarted="letyoucantsee"  />
       <script type="text/javascript">
           function letyoucantsee() {
                $("#youcantsee").css("visibility","hidden");
                 }
       </script>

IE9里面正常运行  用IETESTER进行IE9一下IE的测试时    AsyncFileUpload控件就出现错误 浏览按钮点击没反应

补充：.NET技术 ,  ASP.NET