Consider the following scenario. You have a mixed Microsoft Exchange Server 2003 and Microsoft Exchange Server 2010 environment. You migrate mailboxes from an Exchange Server 2003 server to an Exchange Server 2010 server. In this scenario, certain free/busy messages are not replicated from the Exchange Server 2010 server to the Exchange Server 2003 server. Therefore, the updated free/busy messages of the migrated mailboxes are not available on the Exchange Server 2003 server.
Additionally, the following event is logged in the Application log on the Exchange Server 2003 server:
Event Type: Error
Event Source: MSExchangeFBPublish
Event Category: General
Event ID: 8207
Description: Error updating public folder with free-busy information on virtual machine <server name>. The error number is 0x80070057.