Hi Jaguar,
Please make sure the account used to backup Exchange mailboxes has the following:
1. Member of Domain Admin (if a member of Domain Users - please remove it from this group)
3. Has a Non-hidden (can be seen in Global Address List), active (has received and sent messages) and unique mailbox (unique mailbox = first 5 letters have to be unique)
Once you have done the above, make sure this account is selected to be used when backing up Exchange mailboxes (Job Properties | Resource Credentials).
Remember - in Backup Exec for Windows Servers v11d, you only need to backup Microsoft Exchange Information Store, as you can now restore individual mailmessages/boxes from this Information Store backup, if you have "Enable restore of individual mail messages and folders from information Store backup" selected.
Hopefully, the above will enable you a successful backup of Exchange.
Regards,
Christiane