Re
Essaye plutôt de la façon suivante, cela devrait marché,
Option Explicit
Function FeuilleExiste(Nom$) As Boolean
On Error Resume Next
FeuilleExiste = Sheets(Nom).Name <> ""
Err.Clear
End Function
Sub Transfer_5th_64kmh()
Dim i As Integer
If FeuilleExiste("5th 64 kmh") = True Then
For i = 3 To 1404
Sheets("ideal forces values").Cells(i, 21).Value = Sheets("5th 64 kmh"): Cells(i, 14).Value
Next i
Else: For i = 3 To 1404
Sheets("ideal forces values").Cells(i, 21).Value = Sheets("sources tabel").Cells(i, 99).Value
Next i
End If
End Sub
Voila
@Christophe@