PRB: Error en System.InvalidOperationException al utilizar HttpWebRequest y HttpWebResponse clases en la aplicación con el grupo de subprocesos

using System;
using System.IO;
using System.Net;
using System.Text;
using System.Threading;
using System.Net.Sockets;

namespace threadTest
{
  
	class Class1
	{
		 public static void Main()
		{			
		// Set number of threads to be created for testing.
			int testThreads = 55;
			for(int i=0;i<testThreads;i++)
			{
				ThreadPool.QueueUserWorkItem(new WaitCallback(PoolFunc));
			}
			Console.ReadLine();
		}

		static void PoolFunc(object state)
		{
			int workerThreads,completionPortThreads;
			ThreadPool.GetAvailableThreads(out workerThreads,
				out completionPortThreads);
			Console.WriteLine("WorkerThreads: {0}, CompletionPortThreads: {1}", 
			workerThreads, completionPortThreads);
			Thread.Sleep(10000);
			
			string url ="http://www.msn.com";         
			
			HttpWebRequest myHttpWebRequest ; 
			HttpWebResponse myHttpWebResponse=null ;        
			// Creates an HttpWebRequest for the specified URL.    
			myHttpWebRequest = (HttpWebRequest)WebRequest.Create(url); 
			// Sends the HttpWebRequest, and waits for a response.
			myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();            
			myHttpWebResponse.Close();
		}
	}
}

Imports System.IO
Imports System.Net
Imports System.Text
Imports System.Threading
Imports System.Net.Sockets

Module Module1

   Sub Main()
      'Set number of threads to be created for testing.
      Dim testThreads As Integer = 55
      Dim i As Integer

      For i = 0 To testThreads
         ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf PoolFunc))
      Next
      Console.ReadLine()

   End Sub
   Public Sub PoolFunc(ByVal state As Object)

      Dim workerThreads, completionPortThreads As Integer

      ThreadPool.GetAvailableThreads(workerThreads, completionPortThreads)

      Console.WriteLine("WorkerThreads: {0}, CompletionPortThreads: {1}", workerThreads, completionPortThreads)
      Thread.Sleep(10000)
      Dim url As String = "http://www.msn.com"
      Dim myHttpWebRequest As HttpWebRequest
      Dim myHttpWebResponse As HttpWebResponse = Nothing
      ' Creates an HttpWebRequest for the specified URL. 
      myHttpWebRequest = CType(WebRequest.Create(url), HttpWebRequest)
      'Sends the HttpWebRequest, and waits for a response.
      myHttpWebResponse = CType(myHttpWebRequest.GetResponse(), HttpWebResponse)
      myHttpWebResponse.Close()
   End Sub
End Module