Hier meine eigene Lösung :)

[Rannh]

Vielleicht braucht es jemand:
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Option Explicit

Private Sub Form_Load()

Dim S As String

S = "0a9z"

Dim lngCurrPos As Long
Dim lngCharCode As Long

S = LCase(S)

For lngCurrPos = 1 To Len(S)
    lngCharCode = Asc(Mid(S, lngCurrPos, lngCurrPos + 1))
    If (lngCharCode < 48 Or lngCharCode > 57) And (lngCharCode < 97 Or lngCharCode > 122) Then
        MsgBox "no absolute string"
        Exit For
    End If
Next

End

End Sub