Failed to create MAPI session

Except for the Directory Service and the Admin Service, the Enterprise Vault services and tasks run under the Vault Service account. If you have set up a service or task to run under a different account, or if you have not given the Vault Service account the required Microsoft Exchange Server permissions, an Exchange Journaling Task continues to log errors until you stop it.

The Exchange Journaling Task continues to try to process the Microsoft Exchange Server Journal mailbox at one-minute intervals. This problem shows up in the Windows Event Viewer as follows:

* retry count:
Could not get a MAPI session from the session pool
whilst processing mailbox /o=ACME/ou=Site2000/
cn=Recipients/cn=lvservice

and:

Could not scan user mailbox
/o=ACME/ou=Site2000/cn=Recipients/cn=lvservice,
unable to get the state of the users mailbox

Check the following:

Is the Exchange Server computer running (private message store)?
Has the Enterprise Vault mailbox been deleted?
Have the Vault Service account permissions been set on the Exchange tree?