JS Error with RadWindow and custom print button

[Edward Sudit]

I am using the code posted on this forum for adding a custom print button to the RadWindow title bar.  The code seems to work, but I get an error on the page that seems to be related to issuing the "insertBefore" command.  The code is provided in this post below. 

The error message is:
    Message: Sys.ArgumentUndefinedException: Value cannot be undefined.
    Parameter name: handler
    Line: 2472
    Char: 16
    Code: 0

<telerik:RadScriptBlock runat="server" ID="RadScriptBlock1">
    <script type="text/javascript">
        var radWnd;
        
        function <%=ClientID%>_OpenPrintWindow(url){
            radWnd = radopen(url, null);
            radWnd.set_title('Print Contract Form');
            radWnd.set_modal(true);
            radWnd.setSize(750,500);
            radWnd.center();
            radWnd.set_visibleStatusbar(false);
            radWnd.add_show(OnClientShow());
            radWnd.set_behaviors(Telerik.Web.UI.WindowBehaviors.Move +
                                 Telerik.Web.UI.WindowBehaviors.Close +
                                 Telerik.Web.UI.WindowBehaviors.Resize);
        }
        function OnClientShow()
        {
            var TitleBar = radWnd.GetTitlebar();
            var parent = TitleBar.parentNode;
            var oUL = parent.getElementsByTagName('UL')[0];
            if (!(oUL.firstChild.id == "customprintbuttonID")) // Check if the element is already added
            {
                // If not - create and add the custom button
                oUL.style.width = "192px";
                var oLI = document.createElement("LI");
                oLI.id = "customprintbuttonID"
                var aPrintBtn = document.createElement("A");
                oLI.appendChild(aPrintBtn);
                aPrintBtn.className = "customprintbutton";
                aPrintBtn.href = "javascript:void(0)";
                aPrintBtn.title = "Print Content";
                aPrintBtn.onmousedown = printWin;
                oUL.insertBefore(oLI, oUL.firstChild);
            }
        }

        function printWin(e)
        {
            var content = radWnd.GetContentFrame().contentWindow;
            var printDocument = content.document;
            if (document.all)
            {
                printDocument.execCommand("Print");
            }
            else
            {
                content.print();
            }
            //Cancel event!
            if (!e) e = window.event;

            return $telerik.cancelRawEvent(e);
        }
     </script>        
</telerik:RadScriptBlock>

[Georgi Tunev]

Hi Edward Sudit,

I already answered your other forum thread on the same subject. For convenience I am pasting my reply below. If needed, please, let's continue the discussion in the other thread.

---

The code that you posted is OK and is not raising such error on our side. I believe that the problem might be somewhere else on the page, but without having a better view over your case, I cannot tell for sure.

Please open a support ticket and send me a small sample project where the problem could be reproduced - I will check it right away and do my best to help you.

All the best,
Georgi Tunev
the Telerik team