Option Explicit
 
Public Sub ErrorMessage(Nummer As Long, Beschreibung As String, Quelle As _
  String, Aktion As Long)
    Load frmFehlerfenster
    frmFehlerfenster.SendMessage Nummer, Beschreibung, Quelle, Aktion
    frmFehlerfenster.Show vbModal
End Sub
 
Private Sub cmdFehler_Click()
 
    On Error GoTo errHandler
 
        Dim i As Byte
        i = 3.54325432543437E+15
 
errHandler:
 
        SendMessage CLng(Err.Number), CStr(Err.Description), _
          "frmTest:cmdFehler", 0
 
        frmFehlerfenster.Show
 
End Sub

Private Sub cmdFehlerOK_Click()
    Unload Me
End Sub
 
Sub SendMessage(Nummer As Long, Beschreibung As String, Quelle As String, _
  Aktion As Long)
 
    txtAktion.Text = Aktion
    txtBeschreibung.Text = Beschreibung
    txtNummer.Text = Nummer
    txtQuelle.Text = Quelle
 
End Sub

Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal _
  hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Auf den Sack schl?gt man, den Esel meint man.