Users who perform backups must be either an administrator or a backup operator. Backup operators (or Service Users) have full control of the registry and the installation folder. The LocalSystem Account is the default account used to backup all files.
Make sure that the LocalSystem Account must have read or write access to the files being backed up, or have backup or restore privileges set on the computer where the files reside.
For more information, see Permissions Required for the Windows File System Agent.