The MAPI call 'OpenMsgStore' failed with the following error:
The attempt to log on to the Microsoft Exchange Server computer has failed.
The MAPI provider failed.
Microsoft Exchange Server Information Store
ID no: 8004011d-0512-00000000
This error is logged by the Exchange System Attendant when the information store is not running or when one of the mailbox stores failed to mount.
If your primary email server is an Exchange server and you are monitoring events (e.g. EventSentry), then it is HIGHLY recommended that you setup an alternate email recipient that receives emails from this event (that is not hosted on this Exchange server).
This ensures that you get notified immediately when this critical error occurs.