This Error event indicates that the Microsoft Exchange Server that runs the Client Access server role required to retrieve Schedule+ Free Busy information for the e-mail address specified in the event description could not be found. This event may occur when you have multiple Active Directory sites and one of the Active Directory sites does not have a Client Access server role deployed.

Note:
This event occurs when the diagnostic logging level of Availability Service is set to Low. For more information about how to change diagnostic logging levels, see Change Logging Levels for Exchange Processes.

To resolve this error, follow these steps:

• If you have multiple Active Directory sites that have an Exchange server that runs the Mailbox server role, make sure that each site has the Client Access server role deployed.
  
  
• Review the Application event log for related events. Events that occur immediately before and after this event may provide more information about the root cause of this error.
  
  
• If this event seems to be causing mail flow interruptions or other problems in the Exchange environment, contact Microsoft Product Support. For information about contacting support, visit Microsoft Help and Support Web site.
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.