Hi

Code with a few changes

Sub Steffen()

Open "C:\\Users\Path\" & Sheets(4).Range("C6").Value & ".txt" For Append As #1
    For i = 1 To Sheets(3).UsedRange.Rows.Count
        Print #1, Sheets(3).Cells(i, 1).Value
    Next i
Close #1

On Error GoTo err
Application.DisplayAlerts = False
ActiveWorkbook.SaveAs "C:\Users\Path\" & Sheets(4).Range("C8").Value & ".xlsx", FileFormat:=51
err:
Application.DisplayAlerts = True

End Sub