Hi Lucien,
To answer...
1. AOFO (Advanced Open File Option) needs to be used. This will ensure that any open files on your server are backed up.By default, PSTs will not be backed up without AOFO, causing your backups to either fail, or show as incomplete.
2. Symantec recommend never using AOFO when backing up DBs. My suggestion is to make sure you're: A] using the Exchange agent to back up Exchange, and not do a flat file backup. Active exclusions will make sure that even if you select the folder in which your *.edb is located, it won't be backed up; B] Split your backups. If you don't know how, read up on it here...
https://www-secure.symantec.com/connect/articles/backing-databases-and-files-same-tape-separate-jobs-using-backup-exec
Laters!