How to remove a duplicate activity copy?

In the learning process I selected duplicate activity and now have a copy of system off. On edit this has no - sign to select delete. How do I remove this activity copy ?

This is a bug in version 1.7. If you duplicate the System Off activity, it can’t be deleted. If you get into that scenario, you would need to delete the room (or manually edit the underlying Roomie.plist to remove that section).