To perform the following procedure on a computer that has the Exchange Management Console installed, the account you use must be delegated membership in the local Administrator group on the computer on which you are restoring the database. For more information about permissions, delegating roles, and the rights that are required to administer Exchange 2007, see Permission Considerations.
Make sure that the database you are restoring is not currently mounted. If there is a database present, make sure that you have a copy of it before you overwrite it, and that the database is configured to allow overwrite.