To resolve this warning, do the following:
Increase diagnostic logging so that you can determine which attributes or properties contain invalid values. Specifically, increase the diagnostic logging level on the Validation counter of the MSExchangeADAccess performance object. You can increase logging by running the following Exchange Management Shell cmdlet: Set-EventLogLevel MSExchangeADAccess\Validation -Level High. For detailed information about increasing logging, see How to Change Logging Levels for Exchange Processes.
Review the additional MSExchangeADAccess events in the Application log to determine which attributes or properties contain invalid values.
Important After you have completed troubleshooting this issue, return logging to the default level by running the following cmdlet: Set-EventLogLevel MSExchangeADAccess\Validation -Level Lowest.
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.