How can I receive UDP packets into Unity Webplayer?

I am building a simple webplayer that accept remote user input. However, I can't seem to send anything into it. The programs below compiles file and run fine, but will not receive anything. I tried port 1023 - 25000, no avail. I am running this from Unity Editor. I use free UDP Test tool to send message to 127.0.0.1. When I re-do this code for a C# console application, it works well. But not from Unity Webplayer build. Could someone help?

 using UnityEngine;
 using System.Collections;
 
 using System;
 using System.Net;
 using System.Net.Sockets;
 using System.Threading;
 using System.Text;
 
 public class UDPDemo : MonoBehaviour {
     
     private UdpClient receivingUdpClient;    
     private IPEndPoint remoteIpEndPoint;
 
     private Thread thread;
     
     // port number
     private int receivePort = 843;
     
     // Use this for initialization
     void Start () {
         try {
             receivingUdpClient = new UdpClient(receivePort);
         } catch (Exception e) {
             Debug.Log (e.ToString());
         }
         
         remoteIpEndPoint = new IPEndPoint(IPAddress.Any, 0);
 
         // start the thread for receiving signals
         thread = new Thread(new ThreadStart(ReceiveDataBytes));
         thread.Start();
         
         // debug
         Debug.Log("Thread started");
     }
     
        
     void ReceiveDataBytes() {
         while (true) {
             Debug.Log ("Threading inside while");
             // NOTE!: This blocks execution until a new message is received
             Byte[] receivedBytes = receivingUdpClient.Receive(ref remoteIpEndPoint);
             String receivedStringData = Encoding.ASCII.GetString(receivedBytes);
             Debug.Log ("I received : " + receivedStringData);
             Debug.Log ("The message was sent from " + remoteIpEndPoint.Address.ToString() + " on port number " + remoteIpEndPoint.Port.ToString());
 
             Thread.Sleep(8);
         }
     }
     

     void CloseClient() {
         thread.Abort();
         receivingUdpClient.Close();
     }
     
     void OnApplicationQuit() {
         CloseClient();
     }
 }