WCF / ASMX :: Only Web Services With A [ScriptService] Attribute On The Class Definition Can Be Called From Scr...

I have created a web service. When I check the service directly from it's web page it works correctly. Here's what the code looks like:

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.Configuration;
using System.Runtime.Serialization;
using System.Web.Services;
using System.Web.Services.Protocols;
using System.Web.Script.Services;
using System.Runtime.Serialization.Json;
using System.IO;
using System.Text;
using Microsoft.SharePoint;
using System.Collections;
namespace MDA.WebParts.SPRolodex_Web_Service
{
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
[ScriptService()]
public class SPRolodex_Web_Service : System.Web.Services.WebService
{
public SPRolodex_Web_Service()
{
}
[WebMethod]
[ScriptMethod(ResponseFormat = ResponseFormat.Json)]
public bool ListExists(string personalUrl, string listName)
{
try
{
SPSite mySite = new SPSite(personalUrl);
SPWeb web = mySite.OpenWeb();
SPList list = web.Lists[listName];
return true;
}
catch (ArgumentException)
{
return false;
}
}
}
}

However, when I call the method using ServiceProxy.js (a jQuery based library) I get this error

"Only Web services with a [ScriptService] attribute on the class definition can be called from script."

As you can see the class has the ScriptService attribute and the methods have the ServiceMethod attribute.