Private Sub Command1_Click()
    Dim s As String
    Dim i As Long
 
    s = InputBox("String eingeben:")
 
    For i = 1 To Len(s)
        If Not ((Asc(Mid(s, i, 1)) >= 65 And Asc(Mid(s, i, 1)) <= 90) Or ( _
          Asc(Mid(s, i, 1)) >= 97 And Asc(Mid(s, i, 1)) <= 122)) Then
            MsgBox "Fehler!", vbInformation
        End If
    Next i
End Sub

Gru? Michi aus Hannover

1 + 1 = 3 f?r hinreichend gro?e 1