Cancel is disabled in boot environment while backup process is not running.
Cancel is disabled and reboot or shut-down boot environment failed while backup process is not running.
This is a known issue.
After selecting [Backup], select Cancel to cancel backup process. Then Cancel is enabled.
Or, take the following operating procedures to reboot or shut down boot environment.
1) Press [Ctrl] key and select [F11] while pressing [Tab] key. Then command prompt will start.
2) Run the following command.
> wpeutil reboot
> wpeutil shutdown
– ActiveImage Deploy USB 18.104.22.1682