When you crreate a new mailbox database in exchange 2010 and then complete the process it trysd to mont the database you may see the error below.
Couldn’t mount the database that you specified. Specified database:
<test>; Error code: An Active Manager
operation failed. Error: The database action failed. Error: Operation
with message: MapiExceptionNotFound: Unable to mount database.
Operation failed with message: MapiExceptionNotFound: Unable to mount
This is a known issue with Exchange 2010 and I have seen it in all service packs and updates. The error is due to exchange for some reason not seeing a global catalogue server correctley.
A work around is is to force your exchange server manually to look at your global catalogue server.
1) open up powershell and enter the following