Calendar sync is not working, error "Logon Error -2147221231 The information store could not be (4286455)

The calendar synchronization is not working, and the following error is logged in the calendar agent log file:

 "Logon Error -2147221231 The information store could not be opened.".

The service account Exchange permissions have been verified, and the mail synchronization may be working using the same service account. You may also notice that if you install the agent in the target, it will be unable to connect to the source server. Also, if you install the agent in the source, it will be unable to connect to the target server. If the permissions are correct, why can't the Calendar Synchronization Agent properly connect to the mailbox?

The Calendar synchronization agent connects to both the source and the target information stores. Therefore, if anything such as a firewall is blocking MAPI communication between the source and target servers, the agent will not function correctly. The mail synchronization uses file shares on the source and target servers to transfer mail. If file sharing is allowed through the firewall (even though MAPI may not be), it may work correctly, giving the impression that the calendar synchronization should also work.

Please verify that MAPI communication is not being blocked between the source and target Exchange servers. This can be tested by using MFCMAPI (http://www.microsoft.com/downloads/details.aspx?familyid=55FDFFD7-1878-4637-9808-1E21ABB3AE37&displaylang=en) on the server where the agent is installed,  to logon to the opposite server. If this fails, the Calendar Synchronization Agent will likely also experience problems.

Please note that using Microsoft Outlook to test communication is not a valid test in this scenario, as it uses CDO.dll.  MFCMAPI is needed to duplicate the communication methods of the Calendar Synchronization Agent.