ASP.Net 4.5 AJAX Control Toolkit Accordion Not Working

Dear DotNet Dudes

I cannot get the accordion control to work.

The control appears on my screen with the first pane open, but clicking on headers does not open other panes.

I've spent some time on this and I can't find anything on Google.

I'm sure I've missed something obvious.

Here's my mark-up:

<%@ Page Title="" Language="C#" MasterPageFile="~/Styles/Main.Master" AutoEventWireup="true" CodeBehind="Test.aspx.cs" Inherits="Pembs1.Pages.Test" %>
<asp:Content ID="Content1" ContentPlaceHolderID="cphHead" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="cphBody" runat="server">
<div id="PageContent">
    <ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server"></ajaxToolkit:ToolkitScriptManager>
    <ajaxToolkit:Accordion ID="accTest" runat="server" TransitionDuration="150">
        <Panes>
            <ajaxToolkit:AccordionPane runat="server" ID="apnTest1">
                <Header>
                    Test Head 1
                </Header>
                <Content>
                    Test Content 1
                </Content>
            </ajaxToolkit:AccordionPane>
            <ajaxToolkit:AccordionPane runat="server" ID="apnTest2">
                <Header>
                    Test Head 2
                </Header>
                <Content>
                    Test Content 2
                </Content>
            </ajaxToolkit:AccordionPane>
        </Panes>
    </ajaxToolkit:Accordion>

</div>
</asp:Content>

Any help is greatly appreciated.

Many thanks

Jubbs