Win32 API's WriteFile causes error №6 (invalid handle) for successfully opened mailslot

Hello.

OS: WinXP SP3
IDE: MS Visual C++ 2010 Express Edition
Problem: Transmitter program can't write to mailslot. CreateFile works fine, WriteFile causes error №6 - "invalid handle". Receiver program works fine ("Process Explorer" tool shows me that mailslot exists).

Receiver code:

hMailslot = CreateMailslot(L"\\\\.\\mailslot\\MySendRecv", 0, 2000, NULL);
if (hMailslot == INVALID_HANDLE_VALUE)
  wcout << L"Can't start server" << endl;
else
{
  wcout << L"Server started successfully" << endl;

  DWORD NextSize;
  DWORD MessageCount;
  OVERLAPPED ol;

  while (true)
  {
    auto result = GetMailslotInfo(hMailslot, 0, &NextSize, &MessageCount, NULL);

    if (!result)
      wcout << "Can't get mailslot info" << endl;
    else if (NextSize == MAILSLOT_NO_MESSAGE)
      ;//wcout << "No message to show" << endl;
    else
      while (MessageCount > 0)
      {
        wchar_t* sMsgBuffer = new wchar_t[NextSize+1];
        SecureZeroMemory(sMsgBuffer, sizeof(wchar_t)*(NextSize+1) );

        DWORD NumerOfBytesRead;
        result = ReadFile(hMailslot, sMsgBuffer, NextSize, &NumerOfBytesRead, &ol); 
        
        if (!result)
        {
          wcout << "Can't read message" << endl;
          delete sMsgBuffer;
          break;
        }

        MailslotCallback(sMsgBuffer);

        delete sMsgBuffer;

        result = GetMailslotInfo(hMailslot, 0, &NextSize, &MessageCount, NULL);
        if (!result)
        {
          wcout << "Can't get mailslot info" << endl;
          break;
        }
      }

    Sleep(2000);
  }
}

return 0;

Transmitter code:

void MailslotSend(wchar_t* sMailslotName, void* pData, size_t ndataSize)
{
	HANDLE hFile; 
	
	hFile = CreateFile(sMailslotName,
		GENERIC_WRITE,
		FILE_SHARE_READ,
		0,
		OPEN_EXISTING,
		FILE_ATTRIBUTE_NORMAL,
		NULL);

	if (hFile == INVALID_HANDLE_VALUE) 
	{
		wcout << "Can't begin sending data - error " << GetLastError() << endl;
		return;
	}

	DWORD NumberOfBytesWritten;
	OVERLAPPED ol;
	
	auto fResult = WriteFile(hFile, pData, ndataSize, &NumberOfBytesWritten, &ol);
    if (!fResult)
		wcout << "Data send failed - error " << GetLastError() << endl;
	else
		wcout << "Data send ok" << endl;

	CloseHandle(hFile);
}

int _tmain(int argc, _TCHAR* argv[])
{
	wchar_t msg[64] = {0};

	wcout << "Enter message: ";
	wcin >> msg;

	while ( lstrcmp(L"", msg) != 0 )
	{
		// sending

		MailslotSend(L"\\\\.\\mailslot\\MySendRecv", msg, 64*sizeof(wchar_t) );

		wcout << "Enter message: ";
		ZeroMemory(msg, 64*sizeof(wchar_t) );
		wcin >> msg;
	}

	return 0;
}

Tags: C++, Win32, IPC, MailSlot