1.Restart all Backup Exec Services to make sure the targeted device is online.
2.Make sure the targeted device is enabled, if the devices is not enabled then right click on the device and select Enable.
3.Make sure the device is not in puased state, if the device is in paused then right click and unpause it.
If the Device does not automatically switch to online status, right click and enable online.
Note: This will result in the backup job to immediately start running.