I loaded up a new Exchange 2007 SP1 Server while our production Exchange 2000 Server is still running. I am trying to mount the database in the First Storage Group but keep getting the following error: --------------------------------------------------------Microsoft Exchange Error--------------------------------------------------------Failed to mount database 'Home Office'. Home OfficeFailedError:Exchange is unable to mount the database that you specified. Specified database: MAAT\First Storage Group\Home Office; Error code: MapiExceptionCallFailed: Unable to mount database. (hr=0x80004005, ec=-2147467259). I am starting to wonder if the AD schema was properly extended to for Exchange 2007 because this appears to be some sort of Security Group or Permissions error?????

Check Out:http://support.microsoft.com/kb/925825Event ID 9519 "Error 0x80004005" is logged in the Application log when you try to mount a database in Exchange Server 2010 or in Exchange Server 2007

If your AD schema is bigger could be replication delays, btw try mounting the database using cmdlet with the -force parameter...or force AD replication...CapecolMCSA - MCTS Exchange Server 2007

Please try KB925825 and let us know the result.