Hello,
As we understand that while performing backup on backup-to-disk folder you get a Final error, unknown error has occurred.
If the Device and Media Service is using the local System account and rest all Backup Exec Services are using an account other than Local system account and the backup is targeted to backup-to-disk folder, the backup job fails
To resolve the issue, make sure that Device and Media Service is using same account as being used by other Backup Exec services.
This however does not happen if the job is targeted to Tape drive/library or if all the Backup Exec Services are using the Local system account.
You may also check if the account has exchange admin rights.
Thank You,
Shweta