Can't get Ajax Slideshow extender to work

I am struggling to get the ajax slideshow extender to work.

Can anyone point me in the right direction and tell me what is wrong with this code ...

My WebService code is as follows ...

Imports System.Web
Imports System.Web.Services
Imports System.Web.Services.Protocols

' To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment the following line.
<System.Web.Script.Services.ScriptService()> _<WebService(Namespace:="http://tempuri.org/")> _<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class WebService
    Inherits System.Web.Services.WebService<System.Web.Services.WebMethod()> _<System.Web.Script.Services.ScriptMethod()> _
    Public Shared Function GetSlides() As AjaxControlToolkit.Slide()
        Dim images As New List()
        images.Add(New AjaxControlToolkit.Slide("~/Getting_Started/Screenshots/locum1.JPG", "", ""))
        images.Add(New AjaxControlToolkit.Slide("~/Getting_Started/Screenshots/locum2.jpg", "", ""))
        images.Add(New AjaxControlToolkit.Slide("~/Getting_Started/Screenshots/locum3.jpg", "", ""))
        images.Add(New AjaxControlToolkit.Slide("~/Getting_Started/Screenshots/locum4.jpg", "", ""))
        Return (images.ToArray())
    End Function

End Class

My Page Code is as follows ..

<%@ Page Title="" Language="VB" MasterPageFile="~/sitemaster.master" AutoEventWireup="false" CodeFile="Locum_How.aspx.vb" Inherits="Getting_Started_Locum_How" %><%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="asp" %><asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server"></asp:Content><asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder2" Runat="Server"></asp:Content><asp:Content ID="Content3" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"><p>
        This page will show images of how the system works for Locums ...<asp:ToolkitScriptManager 
            ID="ToolkitScriptManager1" runat="server"></asp:ToolkitScriptManager></p><p><asp:Image ID="HowImages" runat="server" Height="235px" Width="700px" 
            ImageUrl="~/Getting_Started/Screenshots/locum1.JPG" /><asp:SlideShowExtender ID="HowImages_SlideShowExtender" runat="server" 
            AutoPlay="True" Enabled="True" Loop="True" SlideShowServicePath="Locum_Slides.asmx" 
            TargetControlID="HowImages" NextButtonID="NextBttn" 
            PlayButtonID="StopBttn" PreviousButtonID="PrevBttn" 
            SlideShowServiceMethod="GetSlides" StopButtonText="Stop"></asp:SlideShowExtender></p><p><asp:Button ID="PrevBttn" runat="server" Text="Prev" /><asp:Button ID="StopBttn" runat="server" Text="Stop" /><asp:Button ID="NextBttn" runat="server" Text="Next" /></p></asp:Content>

My asmx code is as follows ..

<%@ WebService Language="VB" CodeBehind="~/App_Code/WebService.vb" Class="WebService" %>

Probably something very simple or Very Stupid, but any help would be greatly appreciated.

Regards

Stuart