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.