Hi,
The error message that you have mentioed is generic in nature. Following are some of the reasons that could cause the issue :
1. Anti-virus software accessing the Information Store at the same time as the backup, i.e. using the same Messaging API as Backup Exec does.(It is then recommended to stop Anti-virus software services when backing up the mailboxes).
2. Multiple levels of embedded mail messages (a message attached to a message attached to a message etc.)(remove message)
3. Automated system messages (undeliverable, over size limit etc.)(remove message).
4. The message / attachment is really corrupt (can't open, view or execute)(remove message).
5. Virus infected Information store (clean for virus).
6. Very long subject lines (remove message).
7. Very long attachment names (remove message).
8. Very large attachments (might give out of resource like errors)(remove message).
Check the name of the mailbox (which gives error "is a corrupt file") in job log and download all the mails of that mailbox to personal folder file (.pst )
Should the problem persist after following the above mentioned steps, please revert with the latest updates.
Thanks.