Dim i As Long
Dim bResult As Boolean
 
bResult = False
For i = 1 To 24
  If Me.Controls("chk_" & CStr(i)).Value = Aktiviert Then
    bResult = True: Exit For
  End If
Next i
 
If Not bResult Then 
  MsgBox CStr(i) & ", du mußt mindestens eines auswählen!", vbInformation, _
    "Hinweis"
End If

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