VB2010 Express Net MidiOutOpen Error

'The problem described below has now been solved when I noticed I had stupidly put ByVal lphMidiOut instead of ByRef !!!! Apologies to all.

'I am baffled as to why this program fails

Imports System.Runtime.InteropServices
Public Class Form1
    Declare Function midiOutOpen Lib "winmm.dll" Alias "midiOutOpen" _
        (ByVal lphMidiOut As Int32, ByVal uDeviceID As Int32, _
         ByVal dwCallback As Int32, ByVal dwInstance As Int32, _
         ByVal dwFlags As Int32) As Int32

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
                            Handles Me.Load
        Dim lpMO As Int32
        Dim rv As Int32 = midiOutOpen(lpMO, -1, 0, 0, 0)
        Debug.Print(CStr(rv))

        '''''  the above code returns error 11 (MMSYSERR_INVALPARAM) ?? '''''
        '''''           -1 is the uDeviceID for the MIDI_MAPPER         '''''
        '''''  It also fails for uDeviceID = 0 (my on-board sound card) '''''
    End Sub
End Class

'Anyone got an idea as to why?

Tags: Visual Basic