How to open a popup window when click on AjaxTabpanel in asp.net

I have web application in that I have a ajaxTabedinterface. I want open the pop-window when I click on tab-panel for this. I have created Javascript function and I call this function in tab-panel OnclientClick, and I run the application. Then it doesn't show Tabs it show just white page only. Here I have post my code what I did. Please check it once give me any suggestion where I can change the code .....

Tabpanle

                <cc1:TabPanel runat="server" HeaderText="Documents" OnCli开发者_C百科entClick="openwindow(),return false;" ID="TabPanel4">

         <ContentTemplate> </ContentTemplate>
          </cc1:TabPanel> 

Javascript

   <script type="text/javascript" language="javascript">

    function openwindow() {

        retVal = window.open("AllClients.aspx", null, "left=150px,menubar=no, top=150px, width=800px, height=450px, scrollbars=no, status=no, resizable=no");
        retval.focus();
    }
</script>

Please help me how to open a popupwindow on tabpanel onclient click event...

First, check your OnClientClick definition. When you put "openwindow(),return false;", you should have written "openwindow(); return false;"