Erreur d'exécution 94 utilisation incorrecte de null

Sub affecter_wqtt1()
Dim Lig As Byte, jour As Byte, Folio As String, ppX As String, DerLig
Dim adrqtt As String, f As String
Application.ScreenUpdating = False
With Sheets("acc")
Range("AB52:AB61").Value = Range("Q52:Q61").Value
  DerLig = .Range("AC" & Rows.Count).End(xlUp).Row
  For Lig = 52 To DerLig
    jour = Day(.Cells(Lig, "AB"))
    adrqtt = .Cells(Lig, "P").Address
    f = "='acc'!" & adrqtt
    Folio = .Cells(Lig, "ac")
    ppX = Choose(Lig - 51, "E", "H", "K", "N", "Q", "T", "W", "Z", "AC")
    With Sheets(Folio)
      .Cells(.Range("B7").Offset(jour).Row, ppX).Formula = f
    End With
  Next
End With
  MsgBox "Report des Qtt effectué avec succès"
End Sub

Bonjour,

cette macro s'arrete dans la ligne 13 "ppX = Choose(Lig - 51, "E", "H", "K", "N", "Q", "T", "W", "Z", "AC")" affichant un message de débogage:"erreur d'exécution 94 utilisation incorrecte de null"  

merci d'avance
Windows / Chrome 109.0.0.0