This is one rather rare issue, and over several releases it's becoming extinct, but worth mentioning nevertheless.
The message "Disconnected: Session not activated" appears when service processes of Handy Backup fail to connect to each other.
The general solution is to close the program (including closing it in tray) and restarting services manually via Control Panel => Administrative tools => Services, in the following order:
Novosoft Backup Coordinator 7
Novosoft Notify Service
Novosoft Update Service
The order matters: Coordinator is a main process, Notify links itself to Coordinator, Update links to Notify.