Check and make sure that the device type is set to a supported device. If the type is supported, see config backup logs at Events->Search Config Backup Logs.
Config backups, by default, run once a day at 1AM; so with the time selector, change 'from' time to 1AM.
Usually the problem is either password or connectivity related (telnet/ssh access lists).
You can configure Alarm Notifications (IRISLOG) to be triggered if a backup fails.