I have a Socket Server and a client, but the server will not
always online, so the client will try to connect to server at a proper
inteval, when the server is available, the client will connect to it
auto.
      I design a thread to do this work, every 1 second, it check
Socket.Connected, if it becomes False, the thread invoke asynchrous
BeginConnect, WHEN I TEST THE CLIENT WITHOUT SERVER RUN,
that is to say, EndConnect will never connect to the server. BUG'S
APEAR, after 2 to 3 minutes,
System throw following exception:

System.NullReferenceException was unhandled
 Message="Object reference not set to an instance of an object."
 Source="System"
 StackTrace:
      at System.Net.Sockets.Socket.ConnectCallback()
      at System.Net.Sockets.Socket.RegisteredWaitCallback(Object
state, Boolean timedOut)
      at
System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object
state, Boolean timedOut)

Any one can help me to treat the problem?
BTW, Development Evn.
.NET Framework 2.0
Windows2003 SP1
VS2005

Test Code As Follow;
private void Form1_Load(object sender, EventArgs e)
       {
           while (true)
           {
               try
               {
                   // if i must switch to Socket.Connect(...)?
                   FSocket.BeginConnect("127.0.0.1", 6500, new
AsyncCallback(ConnectCallback), this);
               }
               catch
               {
               }
               System.Threading.Thread.Sleep(1000); // Sleep(100)
will see the exception more quick
           }
       }
       static void ConnectCallback(IAsyncResult ar)
       {
           try
           {
               Form1 This = (Form1)ar.AsyncState;
               This.FSocket.EndConnect(ar);
           }
           catch (SocketException)
           {
           }
       }