Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
If Not Intersect(Columns(2), Target) Is Nothing Then
If Range("C2") = "" Or Range("D2") = "" Then
On Error GoTo fin
Application.EnableEvents = False
Target.ClearContents
MsgBox "Attention..."
End If
End If
fin:
Application.EnableEvents = True
End Sub