Sub Copie()
Nf = ActiveSheet.Name
For i = 1 To Sheets.Count
If Sheets(i).Name = CStr([B4]) Then MsgBox ("Copie IMPOSSIBLE, la feuille " & [B4] & " existe déjà !"): Exit Sub
Next
Sheets("base").Copy After:=Sheets(Sheets.Count)
ActiveSheet.Name = [B4]
Sheets(Nf).Select
End Sub