Hello Pierre,

I have something similar up and running really fine in my project. Where exactly the code above fails for you? Is it showing the confirm dialog window correctly? I have the gut feeling that maybe there is a javascript exception prior to executing the CancelPostBack logic and since everything is wrapped inside try/catch blocks the line with setting CancelPostBack is never reached. Also, using fixed ClientIDs in javascript may not always work, since ClientIDs change when additional controls are added on the page. You may try using

 var MyCtl = document.getElementById("<%= btnApply.ClientID %>");

 In any case, here is the code of my approach which works correctly for me:

<script type="text/javascript">
   
    function itemClickHandler(menuID, itemID)
    {       
        var menuInstance = igmenu_getMenuById(menuID);

        if (!confirm("Do you really want to postback?"))           
            menuInstance.CancelPostBack = true;
        else
            menuInstance.CancelPostBack = false;          
              
    }
   
    </script>
   
    <ignav:UltraWebMenu
        ID="UltraWebMenu1"
        runat="server"
        AutoPostBack="true">      
        <Items>
            <ignav:Item Text="Top Item">
                <Items>
                    <ignav:Item Text="Sub Menu Item"></ignav:Item>
                    <ignav:Item Text="Sub Menu Item"></ignav:Item>
                </Items>
            </ignav:Item>
            <ignav:Item Text="Top Item">
                <Items>
                    <ignav:Item Text="Sub Menu Item"></ignav:Item>
                    <ignav:Item Text="Sub Menu Item"></ignav:Item>
                </Items>
            </ignav:Item>           
        </Items>     
    <MenuClientSideEvents ItemClick="itemClickHandler"></MenuClientSideEvents>
    </ignav:UltraWebMenu>

 Oh, btw, I am using version 7.3.20073.38 

Hope this helps.