We've been seeing this exception:

##### Unhandled Exception while running
System.Exception: WSE104: An asynchronous callback raised an exception. --->
System.InvalidOperationException: Queue empty.
  at System.Collections.Queue.Dequeue()
  at
Microsoft.Web.Services2.Messaging.SoapInputChannel.EndReceive(IAsyncResult
result)
  at
Microsoft.Web.Services2.Messaging.SoapReceivers.OnReceiveComplete(IAsyncResult ar)
  at Microsoft.Web.Services2.AsyncResult.Complete(Boolean
completedSynchronously, Exception exception)
  --- End of inner exception stack trace ---

thrown randomly in our nightly automated tests, and I've spent the last week
isolating it.  This small sample program is fairly consistent at reproducing
the bug:

Project Type: Console Application (.NET Framework Runtime Version 1.1.4322)
References:
* Microsoft.Web.Services2 (Version 2.0.1.0, File Version 2.0.4189.0)
* System (Version 1.0.5000.0, File Version 1.1.4322.2032)
* System.Web (Version 1.0.5000.0, File Version 1.1.4322.2032)

--------------------  SimpleWSE.cs  --------------------

using Microsoft.Web.Services2.Messaging;
using System;

namespace WSEReceiversTest
{
    public class SimpleWSE : SoapService
    {
        private Uri _uri;

        public SimpleWSE()
        {
            string url = "soap.tcp://" + System.Net.Dns.GetHostName() + ":" + 5060 +
"/SimpleWSE";
            _uri = new Uri(url);
        }

        public void Initialize()
        {
            SoapReceivers.Add(_uri,this);
        }

        public void Deinitialize()
        {
            SoapReceivers.Remove(_uri);
        }

    }

}

--------------------  SimpleWSETest.cs  --------------------

using System;
using System.Reflection;
using WSEReceiversTest;

namespace WSEReceiversTest
{
    public class SimpleWSETest
    {
        [STAThread]
        public static void Main()
        {
            try
            {
                CauseQueueException();

                Console.WriteLine("No exception.");
                Console.Out.Flush();
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception:\r\n" + ex.ToString());
                Console.Out.Flush();
            }

            Console.WriteLine("\r\nPress enter to continue.");
            Console.ReadLine();
        }
       
        public static void CauseQueueException()
        {
            SimpleWSE simpleWSE = new SimpleWSE();
            simpleWSE.Initialize();
            simpleWSE.Deinitialize();
            DateTime endTime = DateTime.Now.AddMinutes(5);
            Console.WriteLine("Beginning work.  Work will be completed at
approximately " + endTime.ToString("t"));
            Console.Out.Flush();
            while (DateTime.Now < endTime)
            {
                //Anything can be done within the loop, but time has to pass.
                Assembly.GetExecutingAssembly().GetExportedTypes();
            }
            simpleWSE.Initialize();
        }

    }

}