Public Excel As Object      ' weist auf das Excelobject (Diagramm)
Public Workbook As Object   ' weist auf das ExcelWorkbookobject (Diagramm)
...
 
Private Sub Form_Initialize()
  Dim I As Integer
 
  On Error Resume Next
 
  ' Verbindung zu Excel aufbauen
  Set Excel = GetObject(, "Excel.Application")
  If Error <> "" Or Excel Is Nothing Then
    On Error Resume Next
    Set Excel = CreateObject("Excel.Application")
    If Error <> "" Or Excel Is Nothing Then
      Message 1101, Error
      Unload Me
      End
    End If
    Excel.WindowState = xlMinimized
    Excel.Visible = True
  End If
 
  ' Verbindung zur, im Chart-Control, angezeigten Arbeitsmappe aufbauen
  Chart.Width = picExcel.ScaleWidth
  On Error Resume Next
  [color=red]Set Workbook = Chart.Object        '<<<<<<<< Hier tritt der 
  ' Fehler auf
  If Error <> "" Or Workbook Is Nothing Then
    Message 1102, Error
    Unload Me
    End
  End If
  Excel.Windows(Workbook.Name).Visible = True
 
  ...
 
End Sub

Viel Spass,
R@lf