First, verify that the information store service is started. For the same, you need to right-click My Computer, select Manage>Services and Applications >Services.

  Now, right-click Microsoft Exchange Information Store and select Start.

  Open Exchange System Manager and go to Administrative First Storage Group. Right-click the mailbox store you need to restore and select Dismount Store.

  After dismounting the database, right-click it and select Properties.

  Now, select the Database tab and check This database can be overwritten by a restore.

  Go to Start > Programs > Accessories > System Tools > and then select Backup.

  If the backup you just started runs in wizard mode, choose advanced. Select the Tools tab, choose Restore Wizard, and then click Next.

  A What to restore screen appears. Select and catalog the corrupt backup file.

  Select the mailbox stores and log files to restore and click Next.

  Check your server name under Restore To. Specify a temporary path for all log and patch files. Click Next.

 After completion of the process, go to Exchange System Manager and try mounting the mail store. If the process is successful, you should be able to mount it without getting an error.