This Warning event indicates that a Lightweight Directory Access Protocol (LDAP) search performed by an Exchange component failed. In absence of other events, this event usually means that there is a problem with a specific user or operation. Mail flow should not be affected.

This warning may be caused by the following conditions:

• Domain controller configuration issues
  
  
• Network connectivity problems
  
  
• Permissions problems
  
  

If this event is rarely seen, it can safely be ignored. If this Warning event is logged at specific times or if any other pattern is detected, do the following:

• Check the Application log for related events. The detail in other MSExchange ADAccess events and other events may help determine the root cause of this warning. Increase diagnostic logging for the MSExchange ADAccess\Topology category to Lowest or higher. For detailed information about how to increase logging, see Manage Diagnostic Logging Levels.
  
  
• 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.
  
  

For more information about the Get-EventLogLevel and Set-EventLogLevel diagnostic logging cmdlets, see the following topics:

• get-eventloglevel
  
  
• Set-EventLogLevel
  
  

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.