SlideShow method error

I am trying to use the SlideShowExtender in toolkit and I get the following error.

An unhandled exception occurred:

Message: Unknown web method GetSlides.

Parameter name: methodName

 Stack Trace:

  at System.Web.Script.Services.WebServiceData.GetMethodData(String methodName)

  at System.Web.Script.Services.RestHandler.CreateHandler(WebServiceData webServiceData, String methodName)

  at System.Web.Script.Services.ScriptHandlerFactory.GetHandler(HttpContext context, String requestType, String url, String pathTranslated)

  at System.Web.HttpApplication.MaterializeHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()

  at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)

  at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

Below is my markup and webmethod 

<asp:Image ID="ImgSlide" runat="server" Height="300" Width="300" /><ajaxToolkit:SlideShowExtender ID="SlideShowExtender1" runat="server" 
                    TargetControlID="ImgSlide" 
                    SlideShowServiceMethod="GetSlides" 
                    SlideShowServicePath="~/WebServiceImages.asmx" 
                    AutoPlay="True" 
                    PlayInterval="1000" />

Imports System.IO
Imports AjaxControlToolkit
Imports System.Web.Services

' 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 WebServiceImages
    Inherits System.Web.Services.WebService<WebMethod()>
    Public Shared Function GetSlides() As Slide()
        Dim slides As New List(Of Slide)()
        Dim sPath As String = HttpContext.Current.Server.MapPath("~/ketodocs/slides/")
        If sPath.EndsWith("\") Then
            sPath = sPath.Remove(sPath.Length - 1)
        End If
        Dim pathUri As New Uri(sPath, UriKind.Absolute)
        Dim files As String() = Directory.GetFiles(sPath)
        For Each file As String In files
            Dim filePathUri As New Uri(file, UriKind.Absolute)
            slides.Add(New Slide() With {
              .Name = Path.GetFileNameWithoutExtension(file),
              .Description = Path.GetFileNameWithoutExtension(file) + " Description.",
              .ImagePath = pathUri.MakeRelativeUri(filePathUri).ToString()
        })
        Next
        Return slides.ToArray()
    End Function

End Class