Hello,

You are right, ClientSideEvents are not fired for HeaderClick onMouseRightClick, but you can use this solution:   

    <script type="text/javascript">

        var listBarClientID = "<%= UltraWebListbar1.ClientID %>";             

        var header1 = listBarClientID + "_Group_0_header"; // is always same

        //"_Group_0_header" is hard coded, for next group will increase with 1,

       //e.g. "_Group_1_header", "_Group_2_header", etc

      
       var headerElement = document.getElementById(header1);

       headerElement.oncontextmenu = function(e)

        {

            alert("popup menu here");            

            // cancel events for event to prevent browser

        }

   </script>