The error "At least one root path cannot be found in the backup file" is displayed when a user tries to preview objects in a Security Explorer backup archive file. All the backup archive files are only 1KB in size indicating that the backups are not completing successfully, although the Windows Task Scheduler showed that the Schedule backup task ran and completing successfully.
Manually executing the backup using SXPBackup.exe from the command line, with the same command from the backup schedule with the mapped drive (the one that failed), it executes successfully.

If a scheduled permission backup is created for a share mapped to a drive letter and the Security Explorer NTFS module is used to create the backup schedule, the scheduled backup task runs, but the backup fails with no obvious error.

When the job is executed by the Task Scheduler Service, the mapping (mapped drive) is not allowing the Current Security Principal’s (the account running the service) permission to be validated correctly so the backup failed because access is denied.
Use the Security Explorer Share Permission Module to schedule the backup of the same path using the UNC.
