Error Message

V-79-57344-65280 Unable to restore the selected Microsoft Exchange database 'Mailbox Store' because it is currently mounted. Use the Exchange System Manager to dismount it, and then retry the job.
Connection to the restore target has been lost. Operation canceled.

1. Make sure the Recovery Storage Group Mailbox Store is dismounted. Also make sure that This database can be overwritten is selected on Database tab of the Exchange database. 

2. If the Mailbox Store in the Recovery Storage Group is already dismounted and if you still receive the same error, create the following registry key on both servers, the Media server and the Remote Exchange server (If Exchange server is a remote server)

Warning: Incorrect use of the Windows registry editor may prevent the operating system from functioning properly. Great care should be taken when making changes to a Windows registry. Registry modifications should only be carried-out by persons experienced in the use of the registry editor application. It is recommended that a complete backup of the registry and workstation be made prior to making any registry changes.
 

• HKLM:Software\Veritas\Backup Exec\Engine\ESE Or HKLM:Software\Symantec\Backup Exec For Windows\Backup Exec\Engine\ESE
• Create a New - DWORD Value "ignore mount state" (all in lower case)
• Set the value to 1 (Decimal) 

3. Restart all Backup Exec services on Media Server and Remote Agent service on exchange server. 

4. Run the restore job. If job still fails the contact technical support for further help. 

5. Once the restore completes, remove the registry keys to set servers to its original state.