Private Sub Form_BeforeUpdate(Cancel As Integer)
If MsgBox("Save changes?", vbQuestion + vbYesNo) = vbNo Then
   Cancel = True
End If
End Sub

Private Sub Form_Error(DataErr As Integer, Response As Integer)
   If DataErr = 2169 Then
     Response = acDataErrContinue
   End If
End Sub

Save changes code, prevent you can't save record error

Visual Basic