Hello Mehdi,
Please ensure that the account being used to backup the mailboxes has the following rights:
1. Domain admin rights.
2. Exchange full rights on the site level in exchange.
3. The account has the first five letters unique.
4. The account user has a n active mailbox on the exchange server with mails in it.
5. The user name is visible in GAL global address list.
6. Then try the backup.
Additional Information :
For information on the recent VERITAS Backup Exec security vulnerabilities, including links to the downloads for the necessary hotfixes, please refer to the following document:
Patch summary for Security Advisories VX05-001, VX05-002, VX05-003, VX05-005, VX05-006, VX05-007
http://seer.support.veritas.com/docs/277429.htm
NOTE : If we do not receive your reply within two business days, this post would be marked assumed answeredand would be moved toanswered questions pool.