J'ai modifié la deuxième ligne ainsi, Range("C14:C65536,E14:E65536"), et cela a fonctionné.
Private Sub Worksheet_Change(ByVal Target As Range)
Set Target = Intersect(Target, Range("C14:C65536"), Me.UsedRange)
If Target Is Nothing Then Exit Sub
Dim cel As Range
For Each cel In Target
If cel <> "" Or Cells(cel.Row, "B") <> "" Then Cells(cel.Row, "B") = Now
Next
End Sub