From Xojo Documentation
If True, the scrollbar will be included in the Tab order and can accept the focus. As a result, the scrollbar's FocusRecieved and FocusLost events will be called when appropriate.
Some controls automatically accept focus, e.g. text fields or lists, so they do not have AcceptFocus property.
This code enables the AllowFocus property. It is in the Opening event of the scrollbar: