Типичный код:
    Dim objFaxServer As New FAXCOMEXLib.FaxServer
    Dim objFaxDocument As New FAXCOMEXLib.FaxDocument

    Try
      objFaxServer.Connect("")

    Dim objFaxServer As FAXCOMEXLib.IFaxServer
    Dim objFaxDocument As FAXCOMEXLib.IFaxDocument

    objFaxServer = New FAXCOMEXLib.FaxServer
    objFaxDocument = New FAXCOMEXLib.FaxDocument

    Try
      objFaxServer.Connect("")

    Dim objFaxServer As FAXCOMEXLib.IFaxServer2
    Dim objFaxDocument As FAXCOMEXLib.IFaxDocument2

    objFaxServer = New FAXCOMEXLib.FaxServer
    objFaxDocument = New FAXCOMEXLib.FaxDocument

    Try
      objFaxServer.Connect("")

    If(<XP/2003>)
      Dim objFaxServer As FAXCOMEXLib.IFaxServer
      Dim objFaxDocument As FAXCOMEXLib.IFaxDocument
    Else ' >=Vista
      Dim objFaxServer As FAXCOMEXLib.IFaxServer2
      Dim objFaxDocument As FAXCOMEXLib.IFaxDocument2
    End If

    objFaxServer = New FAXCOMEXLib.FaxServer
    objFaxDocument = New FAXCOMEXLib.FaxDocument

    Dim objFaxServer As Object ' As FaxServer писать нельзя!!!
    Dim objFaxDocument As Object ' As FaxDocument писать нельзя!!!

    If (IsWinVista()) Then
      Dim objFaxServer2 As FAXCOMEXLib.IFaxServer2 = New FAXCOMEXLib.FaxServer
      objFaxServer = objFaxServer2
      Dim objFaxDocument2 As FAXCOMEXLib.IFaxDocument2 = New FAXCOMEXLib.FaxDocument
      objFaxDocument = objFaxDocument2
    Else
      Dim objFaxServer1 As FAXCOMEXLib.IFaxServer = New FAXCOMEXLib.FaxServer
      objFaxServer = objFaxServer1
      Dim objFaxDocument1 As FAXCOMEXLib.IFaxDocument = New FAXCOMEXLib.FaxDocument
      objFaxDocument = objFaxDocument1
    End If

    Try
      objFaxServer.Connect("")

      With objFaxDocument
        'Set the fax body
        If (IsWinVista()) Then
          Dim arr(1) As String
          arr(0) = FileName
          arr(1) = FileName2
          .Bodies = arr 'тестово объединяем 2 файла (доступно только в IFaxDocument2)
        Else
          .Body = FileName
        End If

Dim WithEvents g_objFaxServer As FAXCOMEXLib.FaxServer

  Dim WithEvents g_objFaxServer As Object 'FAXCOMEXLib.FaxServer
...
  Private Sub frm1_Load(sender As Object, e As EventArgs) Handles Me.Load
...
    Try
      If sys_WinVista Then
        Dim iFaxServer2 As FAXCOMEXLib.IFaxServer2 = New FAXCOMEXLib.FaxServer
        g_objFaxServer = iFaxServer2
      Else
        Dim iFaxServer1 As FAXCOMEXLib.IFaxServer = New FAXCOMEXLib.FaxServer
        g_objFaxServer = iFaxServer1
      End If
      'g_objFaxServer = New FAXCOMEXLib.FaxServer
      AddHandler CType(g_objFaxServer, FAXCOMEXLib.FaxServer).OnServerShutDown, AddressOf Me.g_objFaxServer_OnServerShutDown
...

  Private Sub TimerMSFax_Tick(sender As Object, e As EventArgs) Handles TimerMSFax.Tick
    If (FaxServerSost = False) AndAlso IsServiceExists("fax") _
     AndAlso (GetServiceStatus("fax") = ServiceControllerStatus.Running) Then
      Try
        'Connect to the local fax server.
        g_objFaxServer.Connect("")
        'Now register for the desired events.
        g_objFaxServer.ListenToServerEvents(FAXCOMEXLib.FAX_SERVER_EVENTS_TYPE_ENUM.fsetFXSSVC_ENDED + _
                                            FAXCOMEXLib.FAX_SERVER_EVENTS_TYPE_ENUM.fsetOUT_QUEUE + _
                                            FAXCOMEXLib.FAX_SERVER_EVENTS_TYPE_ENUM.fsetOUT_ARCHIVE)
        FaxServerSost = True 'успешно подключились к факс-серверу
        Debug.Print("Connected")
        MsgBox("Connected")
      Catch
        'ошибка подключения к факс-серверу
      End Try
    End If
  End Sub

  Private Sub g_objFaxServer_OnServerShutDown(pFaxServer As FAXCOMEXLib.FaxServer) ' Handles g_objFaxServer.OnServerShutDown
    FaxServerSost = False 'произошло отключение от факс-сервера
    Debug.Print("Disconnected")
    MsgBox("Disconnected")
  End Sub

Exeption from HRESULT: 0x80040200

Dim objFaxServer As IFaxServerN

 Dim WithEvents g_objFaxServer As FAXCOMEXLib.FaxServer