Failed Verita backup-Directory not found

Backup software: Veritas 9.1
Backup is of the MS Exchange Server.
Log shows failed backup with the message ‘Directory not found’ and then lists the location of a mailbox of a disabled user. In the properties of the disabled user, the checkbox for mailbox is hidden from exchange tasks in marked. Since it is good practice not to delete a users’ mailbox although they are no longer with the company, I have not. I am wondering why the backup is still looking for that directory? There must be a setting I can change somewhere…