Sub WorkSheet_Activate()
Application.CommandBars.FindControl(ID:=21).Enabled = False
End Sub

Option Explicit
Private Sub Workbook_SheetSelectionChange(ByVal Sh As Object, _
ByVal Target As Excel.Range)

Select Case Application.CutCopyMode
Case Is = False
'do nothing
Case Is = xlCopy
'do nothing
Case Is = xlCut
MsgBox "Please DO NOT Cut and Paste. Use Copy and Paste; then delete the source."
Application.CutCopyMode = False 'clear clipboard and cancel cut
End Select

End Sub