findcontrol method contains null reference

[cognos s]

I am trying to use radwindow in the content page of .net web application. I am using this piece of code as suggested in documentation.

 function ShowExisting3() {
        var oWnd = $find("RadWindow1");
        oWnd.show();
    }

 <telerik:RadWindowManager ID="RadWindowManager1" runat="server">
           <Windows>
               <telerik:RadWindow
                   ID="RadWindow1"
                   runat="server"
                   NavigateUrl="http://www.google.com">
               </telerik:RadWindow>             
           </Windows>
 </telerik:RadWindowManager>
   
        <button onclick="ShowExisting3();return false;"  style="width: 190px">
           Show window (using show)</button>


oWnd contrains null value. any suggestions how to get reference to radwindow?

[cognos s]

I found the solution.

var oWnd = $find("<%= RadWindow1.ClientID %>");
          oWnd.show();