It has been observed that in some cases Backup Exec may unintentionally dismount an Exchange 2010 database when you attempt to restore granular items from a GRT-enabled backup.
V-79-57344-65284 - Unable to restore the Microsoft Exchange storage group Test. One or more of its databases have not been enabled for overwrite. Use the Exchange Management Console to enable the property 'This database can be overwritten by a restore' for the databases that you want to restore.
A hotfix is now available for this issue in the current version(s) of the product(s) mentioned in this article. Refer to the Hotfix link under Related Articles at the end of this article to obtain the hotfix needed to resolve the issue.
Backup Exec 2012 Rev 1798 Hotfix 213186 (TECH213186)
Backup Exec 2012