Unknown Web Method

Question

I'm trying to implement a view tracking web service on my website. I'm using JavaScript because I want to exclude any search bots from my tracked views. The problem is I'm getting a "Unknown web method" error when I try to use jQuery to post to the web service I've created.

$(document).ready(function() {

  $.ajax({
    type: "POST",
    url: '<%=ResolveUrl("~/WS/ItemViewTrackingService.asmx/TrackItemView") %>',
    data: "{'itemType': 'thread', 'itemId':<%=mThread.ThreadID %>}",
    contentType: "application/json; charset=utf-8"
  });

});

Here is the web service.

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

<System.Web.Script.Services.ScriptService()> _
<System.Web.Services.WebService(Namespace:="http://tempuri.org/")&gt; _
<System.Web.Services.WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<ToolboxItem(False)> _
Public Class ItemViewTrackingService
  Inherits System.Web.Services.WebService

  <WebMethod(EnableSession:=True)> _
  Public Shared Sub TrackItemView(ByVal itemType As String, ByVal itemId As Int32)

    If itemType.Equals("column", StringComparison.OrdinalIgnoreCase) Then
      Services.ViewTrackingService.TrackColumnView(itemId)
    ElseIf itemType.Equals("thread", StringComparison.OrdinalIgnoreCase) Then
      Services.ViewTrackingService.TrackThreadView(itemId)
    End If

  End Sub

End Class

The error is an ASP .NET error: Unknown web method TrackItemView. Parameter name: methodName

I've done this hundreds of times (seemingly), but I just can't see what I'm missing. I'm sure it's something small...