I got a fresh installed Exchange 2010 and I just wanted to add one more database. I could do Everything else but when adding a database I got the error:

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Microsoft Exchange Error
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Failed to mount database ‘Mailbox’.
Mailbox
Failed
Error:
Active Directory operation failed on bdc3.propel.com. This error is not retriable. Additional information: Access is denied.
Active directory response: 00000005: SecErr: DSID-03151E04, problem 4003 (INSUFF_ACCESS_RIGHTS), data 0
The user has insufficient access rights.

The solution was simple after an hour on google and in the forums.

Just re-run the setup with /preparedomain and it will solve the problem.

Or actually it created the database just fine, but didn’t mount it.. So just wait a few minutes and then try again and it will mount.