Close Mutex of another process

Hi,
I need to close mutex created by another appication. Here is my code:

bReturnVal = CreateProcess(
            NULL,
            "C:\\Program Files\\Skype\\Phone\\Skype.exe",
            NULL,
            NULL,
            FALSE,
            dwCreationFlags,
            NULL,
            NULL,
            &si,
            &process_info);

    if (bReturnVal = 0)
    {
        return 1;
    }

    Sleep(4000);

    HANDLE skypeOriginalMutex = OpenMutex( MUTEX_ALL_ACCESS, false, "SkypeMutex" );
    if ( skypeOriginalMutex != NULL)
    {
        HANDLE res;
        DuplicateHandle(process_info.hProcess, skypeOriginalMutex, GetCurrentProcess(), &res, 0, false, DUPLICATE_CLOSE_SOURCE);
        CloseHandle(res);
        GetLastErrorLoc();
        MessageBox(NULL, "Mutex released", "WOW", MB_OK);
    }

The problem is that original handle is not closed. Please explain how can I close it?
Regards

check if this helps:

It looks like you duplicated and closed a handle in Skype.exe, that had the vaue returned by OpenMutex in your process.  (In other words, it looks like you're duping / closing some random handle in skype.exe.)

One more thing. Due to MSDN:
DUPLICATE_CLOSE_SOURCE - Closes the source handle. This occurs regardless of any error status returned. So the skype mutex have to be closed but it is not.

The mutex that is attached to my process after duplicatehandle executed is "SkypeMutex". Also I see that reference count to SkypeMutex in skype.exe process is incremented. That's the only ways I can verify it's needed handle.