[Tizio]

Hi, I tried to use that command with VisualBasic and I had an error message too :?
Probably I really lack of programming knowledge if I'm not able to make it work that way if I don't use C++...

This is the WORKING routine that I use with VB, I hope you'll find it useful (lines starting with ' are comments):

Public Sub BSPOpenFile(FileName As String)
    Dim cds As COPYDATASTRUCT
    
    'Find BSplayer window's handle
    bsp_hand = FindWindow("BSPlayer", 0&)
    'If BSplayer is running -> window found
    If bsp_hand <> 0 Then
            
        'Set OpenFile as action
        cds.dwData = BSP_OpenFile
        'Create and set the pointer to the file name string
        '(VB doesn't provide pointers like C does)
        cds.lpData = lstrcpy(FileName, FileName)
        'Set the string lenght
        cds.cbData = Len(FileName) + 1
        
        'Open the selected file
        ReturnCode = SendMessage(bsp_hand, WM_COPYDATA, 0&, cds)
        
    End If
End Sub

EDIT:
Almost forgot, if you use WM_BSP_CMD instead of WM_COPYDATA in the send message call BSplayer knows that you are sending a command and not a copydatastruct