When backup source is specified by [folder] or an external hard disk is specified as the backup destination, make sure that the folder exists or the external hard disk is connected and can be properly recognized.

The drive used as the backup destination may have insufficient available space.
Clear sufficient space on the drive to be used as the backup destination and try again.

Try to run [Check Disk] in the setup screen to check the built-in hard disk or a specifically formatted external hard disk, or connect to the computer and run [Scan Disk] to check an external hard disk in FAT format.

When the drive which a backup destination shoring, exists is FAT format, there is a limitation on the maximum file size. Backup will not run if any file exceeds this limitation. In that case, eliminate the file from backup.

(Remote Backup)
To find out the cause of the problem, try backup with a small file first.
Try to access a sharing of remote backup source host from Windows using a specified user name and password.
If you cannot access it, check the access right and user settings for the shared drive, then try accessing it from Windows again.
After you have done so, reconfirm the settings of remote backup and try again.