A duplicate appointment item is created when a user accepts a meeting request in Outlook Web Access

Consider the following scenario:

• You send a single-instance exception meeting request to a Microsoft Exchange Server 2003 user.
  
  Note A single-instance exception meeting request occurs when you modify any field in one instance of a recurring meeting request.
• A Collaboration Data Objects (CDO) 1.21-based application calls the GetAssociatedAppointment method on the meeting request.
• The CDO 1.21-based application calls the Update method on the resulting appointment item.

In this scenario, a tentative meeting request is created in the user's calendar. This tentative meeting request shows both a RecurrenceID and the correct date. However, the time of the tentative meeting request is always set to midnight. When the user later accepts the meeting request in Microsoft Office Outlook Web Access, a duplicate appointment item is created in the Outlook Web Access calendar.

This problem occurs if the Outlook Web Access client queries the user's calendar for a matching item based on the RecurrenceID. However, the value of the RecurrenceID is incorrect based on the tentative item that is created by the CDO 1.21-based application. Therefore, because the Outlook Web Access client cannot find the appointment item, the Outlook Web Access client creates a new appointment item.

To work around this problem, manually delete the duplicate appointment.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.