ArgumentTypeException with OnClientButtonClicking

[Cheryl]

Hello,

I have a RadToolbar and a div that should load contents of another page using jquery.  Does anyone know why this error occurs:
SysArgumentTypeException
Object of type 'Telerik.Web.UI.RadToolbarCancelEventArgs' cannot be converted to type 'Sys.CancelEventArgs'

Any help would be appreciated!

<telerik:RadScriptManager ID="tmgRSM" runat="server" EnableCdn="true">
            <Scripts>
               <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.Core.js" />
               <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQuery.js" />
               <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQueryInclude.js" />
           </Scripts>
        </telerik:RadScriptManager>

        <telerik:RadToolBar ID="radToolBar1" runat="server"
                Width="100%" EnableViewState="false" OnClientButtonClicking="OnToolBarButtonClick">
                <Items>
                    <telerik:RadToolBarButton Text="Tab1" CommandName="Tab1" CheckOnClick="true" Checked="true"></telerik:RadToolBarButton>
                    <telerik:RadToolBarButton IsSeparator="true"></telerik:RadToolBarButton>
                    <telerik:RadToolBarButton Text="Tab2" CommandName="Tab2" CheckOnClick="true"></telerik:RadToolBarButton>
                </Items>
        </telerik:RadToolBar>

        <div id="contentDiv" style="padding-left:20px"></div>

        <telerik:RadCodeBlock runat="server" ID="RadCodeBlock1">
            <script type="text/javascript">
                window.$ = $telerik.$;

                $(document).ready(function () {
                    $('#contentDiv').load('Content.aspx');
                });

                function OnToolBarButtonClick(sender, args) {
                    alert(args.get_item().get_commandName());
                }
            </script>
        </telerik:RadCodeBlock>