class function MessageDlg(MessageText: string; MessageHeader: string; MsgType: TMsgDlgType; Buttons: TMsgDlgButtons; MessageColor: Integer = clBlack; Parent: TForm = nil): Integer; overload;
...
function TfoBaseDialog.ShowDialog(MessageCaption: string; MsgType: TMsgDlgType; Buttons: TMsgDlgButtons; MessageLines: TStrings; Help: LongInt = 0; MessageColor: Integer = clBlack; Parent: TForm = nil): Integer;
var
  I: Integer;
begin
  FMessageHeader := MessageCaption;
  FMessageLines := MessageLines;
  Self.PopupParent := Parent; // vor der Positionierung!

  pngil32.GetIcon(Ord(MsgType), imgTop.Picture.Icon);
  if MessageCaption > '' then
  begin
    lblTop.Caption := MessageCaption;
  end
  else
  begin
    case MsgType of
      vmtAlert:
        lblTop.Caption := 'Warnung';
      vmtInformation:
        lblTop.Caption := 'Information';
      vmtError:
        lblTop.Caption := 'Fehler';
      vmtQuestion:
        lblTop.Caption := 'Frage';
      vmtOpen:
        lblTop.Caption := 'Öffnen';
      vmtSave:
        lblTop.Caption := 'Speichern';
    end;
  end;

  CreateButtons(Buttons);

  for I := 0 to FButtonList.Count - 1 do
  begin
    TButton(FButtonList[0]).Left := ClientWidth - 5 - (FButtonList.Count * 75) - ((FButtonList.Count - 1) * 5);
    if I > 0 then
    begin
      TButton(FButtonList[I]).Left := TButton(FButtonList[0]).Left + ((I * 75) + (I * 5));
    end;
  end;

  // Position bezogen auf Parent
  if Assigned(Parent) then
  begin
    Self.Top := Parent.Top + Floor(Parent.Height / 2) - Floor(Self.Height / 2); // mittig
    Self.Left := Parent.Left + Floor(Parent.Width / 2) - Floor(Self.Width / 2); // mittig
  end
  else
  begin
    Self.Position := poScreenCenter;
  end;

  Self.ShowModal;
  Result := FDialogResult;
end;

procedure TfoPreferences.DoOnLoadError(Sender: TObject; ErrorType: TBlubbErrorType; FileName: string); // Parent Form
begin
  case ErrorType of
    etLoadFile:
    begin
      TBlubbMessageDialog.MessageDlg(Format(conErrorLoadFile, [QuotedStr(FileName)]), conTextOpen, vmtError, [buOk], clBlack, Self);
    end;
  end;
end;