To resolve the error, the duplicate folders that were created by Outlook in the user's mailbox must be manually deleted. To delete the duplicate folders, the administrator or the user can logon to the affected mailbox using Microsoft Office Outlook Web Access or using a MAPI client such as Outlook and follow these steps:
Switch to Folder List view.
Look for the view option in the left bottom section of the UI.
Delete the duplicate folders specified in the event description.
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.