AJAX :: Designer View Shows Accordion Error

I have an Error in the design view when I use the ajax toolkit. it says rendering Control Accordion - An unhandled exception has occurred. Collection was modified; enumeration operation may not execute. I have the relevant service pack, download ajax toolkit and I have used the appropriate declerations on the top of the page, I hope. I haven't yet even put anything on the page and the designer view shows the above error.

<%@ Page Language="vb" AutoEventWireup="false" MasterPageFile="~/Site.Master" CodeBehind="listaccessoriesbytype.aspx.vb" Inherits="FashionPrototypeProject.listaccessoriesbytype"
title="Untitled Page" %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="cc1" %>
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<cc1:Accordion ID="Accordion1" runat="server">
<Panes>
<cc1:AccordionPane ID="ac" runat="server">
<Header></Header>
<Content></Content>
</cc1:AccordionPane>
</Panes>
</cc1:Accordion>
</asp:Content>

I entered this manually in my webconfig: added this under the rest of asssemblies code

<assemblies>
<add assembly="AjaxControlToolkit, Version=3.0.30930.28736, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e"/>
</assemblies>

added under the rest of controls

<controls>
<add tagPrefix="ajaxToolkit" namespace="AjaxControlToolkit" assembly="AjaxControlToolkit, Version=3.0.30930.28736, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e"/>
</controls>