In Office Communicator 2007 R2, User A gets a failure-to-deliver message after sending an IM to User B even though User B receives the message

In a group IM session in Office Communicator 2007 R2, User A sends User B an instant message (IM). User B receives the IM successufly. However, User A still gets a failure-to-deliver message that states that his IM has not been received by User B.

This issue occurs because the 202 Accept message and the Notify message that are sent for the IM are received in reverse order.

To resolve this issue, apply the following update:

• 967673  (http://support.microsoft.com/kb/967673/ ) Description of the Communicator 2007 R2 hotfix rollup package: April 2009

After you apply this update, an Accept message that has been received for the message above is placed in the queue and a check is made for the matching Notify message. When this message is found, the Accept message is taken out of the queue, and the process proceeds as if the message has just been received.

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