Sockets: recv=-1 BUT WSAGetLastError=0 (??)

Hi everyone!

Something weird is happening with an application of mine:
It works OK on any computer but on one (I have nearly one hundred
installations made, up and running).
The computer on which it is not running is: WinXP professional 2002 SP2 on
AMD Athlon64

Mainly my app is a TCP server.
Each client has a listening thread with a loop and a call to the platform
SDK Windows sockets blocking (synchronous) "recv" function
(http://msdn2.microsoft.com/en-us/library/ms740121.aspx) -code below.

According to MS documentation when function "recv" returns SOCKET_ERROR
(-1), an error can be therefore retrieved with WSAGetLastError.
As you can see, I check WSAGetLastError immediately after returning recv.
This works perfectly in every computer.
But on this very one computer out of 100, several times a day, "recv"
returns SOCKET_ERROR (-1), BUT WSAGetLastError returns 0 (!!!)
Sniffing the TCP traffic via Ethereal software I can see that, in fact, the
TCP connection is still up: so it is the "recv" function that is telling me
a lie.

Has this happened to anyone out there?
Have you find any Windows or Athlon64 known bug regarding this matter
(recv=-1 but WSAGetLastError=0)?
Can you think of a way to make my application work on this problematic
computer?

Thank you very much!

Ricardo V?zquez.
Madrid, Spain.

--------------- CODE ---------------
int CClientThread::Run()
{
 char msg[maxLen];

 while (!bExit) {
  int nRet = recv(clientSocket, msg, maxLen, 0);
  if (nRet == SOCKET_ERROR && bExit) {
   // Stop closes clientSocket on exit. WSAETIMEDOUT
   err.Format("Stop closes clientSocket on exit");
   g_logSystem.logWarning(0, err);
   break;
  }
  else if (nRet == SOCKET_ERROR)
  {
   int nErr = WSAGetLastError();
   if (nErr == 0)
    {
    err.Format("recv=-1 but WSAGetLastError=0 from client %s on socket
%ld.", clientId, clientSocket);
    g_logSystem.logWarning(0, err);
    continue;
    }
   else
    {
    err.Format("Connection lost with client %s on socket %ld. Error code
%ld: recv() = SOCKET_ERROR", clientId, clientSocket, nErr);
    g_logSystem.logWarning(0, err);

    closesocket(clientSocket);
    server->DeleteClient(clientSocket);
    cti_RemoveEventListener(this);
    return SOCKET_ERROR;
    }
  }
  else if (!nRet) {
   // Connection has been gracefully closed.
   err.Format("Client %s with socket %ld has closed the connection: recv() =
0 (apparently)", clientId, clientSocket);
   g_logSystem.logNormal(0, err);

   closesocket(clientSocket);
   server->DeleteClient(clientSocket);
   cti_RemoveEventListener(this);
   return 0;
  }
  else {
   // Proccess message:
   msg[nRet] = 0x0;
   err.Format("[Cli %ld] Received: %s", clientSocket, msg);
   g_logSystem.logNormal(4, err);

   CString sMensaje;
   sMensaje = CStrTok(msg, "%");
   while (!sMensaje.IsEmpty())
    {
    parse(sMensaje);
    sMensaje = CStrTok("", "%");
    }
  }
 }
 return 0;
}