callback message - haster

Hej
Jeg vil gerne modtage messages fra et andet program ind i mit program. Det kan jeg osse godt finde ud af med denne kode men der opstår en fejl i kernel når jeg afslutter.

Public Declare Function CallWindowProc Lib \"user32\" Alias \"CallWindowProcA\" (ByVal lpPrevWndFunc As Long, ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Public Declare Function SetWindowLong Lib \"user32\" Alias \"SetWindowLongA\" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

Public Const GWL_WNDPROC = -4
Global lpPrevWndProc As Long

Public Sub Hook(xHwnd As Long)
    lpPrevWndProc = SetWindowLong(xHwnd, GWL_WNDPROC, AddressOf WindowProc)
End Sub

Public Sub Unhook(xHwnd As Long)
  Dim temp As Long
  temp = SetWindowLong(xHwnd, GWL_WNDPROC, lpPrevWndProc)
End Sub

Function WindowProc(ByVal hw As Long, ByVal uMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long

        If uMsg = WM_USER + 308 Then
            Label2.Caption = 1024 + 308 & \" er kommer ind\"
        End If
       
      WindowProc = CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, lParam)
End Function


Form_load: Hook me.hwnd
form_unload: Unhook me.hwnd