This Error event indicates that the Microsoft Exchange File Distribution service could not find the offline address book (OAB) object in Active Directory. The File Distribution service is used to distribute OAB files and custom Unified Messaging prompts. This event may occur when one or more of the following conditions are true:

• The Exchange server that logged this event is trying to connect to a domain controller that is not working correctly.
  
  
• Network issues interfere with attempts to connect to the domain controller.
  
  

The File Distribution service will continue to try to read the OAB object from Active Directory on an hourly interval. However, if this event frequently occurs, follow one or more of these steps:

• Use the Ping or PathPing command-line tools to test basic connectivity. Use Ping to isolate network hardware problems and incompatible configurations. Use PathPing to detect packet loss over multiple-hop trips. For more information, see Microsoft Knowledge Base article 325487, How to troubleshoot network connectivity problems.
  
  
• Run the Dcdiag command line tool to test domain controller health. To do this, run dcdiag /s:<Domain Controller Name> at a command prompt on the Exchange server that generated the event. Use the output of Dcdiag to discover the cause of any failures or warnings that it reports. For more information, see Dcdiag.
  
  
• Review the Application log and System log on your Exchange 2010 servers 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.
  
  
• Review the Operations Console in Operations Manager for detailed information about the cause of this alert. For more information, see the "Introduction" section in this article.
  
  
• Resolve your issue by using self-support options, assisted support options, and other resources. You can access these resources from the Exchange Server Solutions Center. From this page, click Self-Support Options in the navigation pane to use self-help options. Self-help options include searching the Microsoft Knowledge Base, posting a question at the Exchange Server forums, and others. Alternatively, in the navigation pane, you can click Assisted Support Options to contact a Microsoft support professional. Because your organization may have a specific procedure for directly contacting Microsoft Technical Support, be sure to review your organization's guidelines first.
  
  

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.