I have an elderly neighbour with one of these units. It works well except the other neighbour's new Chamberlain unit's remotes open both doors. I can't clear the memory of the Craftsman no matter how long I press and hold the Learn Button. Also, it will only accept one remote at a time. When we program one remote it cancels the other, and vice versa. Can anyone help? John. greatplanes@sasktel.net