Q. Why I cannot move Orange Diary to SD card?
A. If you move Orange Diary to SD card, alarm, backup and export will not work.
This is a limitation of Android operating system and we cannot solve it in our application level.
Since SD card is detachable storage, Android handles the life cycle of the apps in SD card differently and limits some features. Android listed those features in following online documentation with details.
Among the features, Orange Diary is using Service, Alarm service, Broadcast Receivers.