Veritas Backup Exec Mailbox Backup

Hi,

I have a problem here. We are running Backup Exec ver 8 on one of our Exchange Servers to do the Exchange backups. The problem is that we cannot get it to do PST(mailbox) backups. Everytime we try to connect to a server, it asks for a Unique mailbox to connect to. I have created a mailbox specifically for that use, and made the primary NT account the same one we use for the backup services. Thing is, it does not want to accept it, whatever i do. I have even installed Outlook 2000 on the server, and created a profile with the Backup mailbox as the primary mailbox, to no avail. I would appreciate any help in this matter.

We are running Windows NT server 4.0 and Microsoft Exchange 5.5 on a dual Pentium III 450 with 192 MB ram.