When you create a new database in a new Exchange 2010 environment following error occurs when trying to mount it.
Event ID – 15, Source – MSExchangeRepl
Active Manager failed to mount database DB2 on server servername.domain.org. Error: An Active Manager operation failed. Error: The database action failed. Error: Operation failed with message: MapiExceptionNotFound: Unable to mount database. (hr=0x8004010f, ec=-2147221233)
Make sure that the database points to the correct Public Folder Database and has the Offline Address Book selected. After you have do the above, the database will mount correctly.