This Error event indicates that the Availability service was unable to contact the Microsoft Exchange Information Store service (MSExchangeIS) to retrieve free and busy information. This can happen if MSExchangeIS is not running, has failed, or cannot be contacted by this server.
To resolve this Error event, do one or more of the following:
Review the System log for any unexpected MSExchangeIS service errors.
Review the Application log for any indication of MSExchangeIS errors.
Ensure that MSExchangeIS is running from the Services console.
Review the Application log for related events. For example, events that occur immediately before and after this event may provide more information about the root cause of this error.
If you are still having difficulty resolving the issue, contact Microsoft Product Support. For information about contacting support, visit the Contact Us page of the Microsoft Help and Support Web site.
If you are not already doing so, consider running the tools that Microsoft Exchange offers to help administrators analyze and troubleshoot their Exchange environment. These tools can help you make sure that your configuration is in line with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. Go to the Toolbox node of the Exchange Management Console to run these tools now. For more information about these tools, see Toolbox in the Exchange Server 2007 Help.