problem with ReadFile using Overlapped I/O in VC++

Hi,

I'm opening the com port using overlapped I/O, setting the Comm read
timeouts as MAX_DWORD,0,0.

And my Asynchronous read file logic is something like this,

1) Call ReadFile
2) If error == ERROR_IO_PENDING
        ::WaitForSingleObject(lpOverlapped->hEvent,300);

I'm trying to wait for the event to get signalled or timeout after 300
mSec. But i noticed that this function is returning 0x0 which means
WAIT_OBJECT_0 i.e. the event is signalled. But when i do
GetOverlappedResult to read the number of bytes read it is returning
as 0.

How can this happen?. The Event should get signalled only when the
ReadFile has some data in it?. What is the problem here.

I dont want the ReadIntervalTimeouts to be set to some values in order
to get this overlapped I/O working. If i had to use the
ReadIntervalTimeouts , then i can use the normal non-overlapped I/O.

Appreciate your help

Below is my sample code

CreateFile(arrPort, GENERIC_READ | GENERIC_WRITE, 0, //
exclusive access,NULL, // no security
            OPEN_EXISTING,
            FILE_FLAG_OVERLAPPED, NULL);

CommTimeouts.ReadIntervalTimeout = MAX_DWORD
CommTimeouts.ReadTotalTimeoutConstant = 0;
CommTimeouts.ReadTotalTimeoutMultiplier = 0;

if((!::ReadFile(hCom,pBuf,256,pdwRead,lpOverlapped)) || (!*pdwRead))
 {
      lLastError = ::GetLastError();
      // Overlapped operation in progress is not an actual error
      if (lLastError != ERROR_IO_PENDING)
      {
    return -1;
       }

     // Wait for the overlapped operation to complete
   dwovstatus= ::WaitForSingleObject(lpOverlapped->hEvent,dwTimeout);
   switch (dwovstatus)
    {
       case WAIT_OBJECT_0:
    if (!::GetOverlappedResult(hCom,lpOverlapped,pdwRead,FALSE))
    {
        return -1;
    }
  }