Option Explicit
Private Sub Worksheet_Change(ByVal Target As Excel.Range)
Set Target = Intersect(Target, Columns("A"))
If Target Is Nothing Then Exit Sub
Dim rngCell As Excel.Range
On Error GoTo SafeExit
Application.EnableEvents = False
For Each rngCell In Target.Cells
If Trim$(rngCell.Value) <> "" Then
rngCell.Offset(, 1).FormulaR1C1 = "=VLOOKUP(RC[-1],Stammdaten!C[-1]:C,2,TRUE)"
End If
Next
SafeExit:
Application.EnableEvents = True
End Sub