Error message when you send two messages in Communicator 2005: "The following message could not be delivered to all recipients"

When you send two messages over TCP transport in Microsoft Office Communicator 2005, the second message cannot be delivered to the recipient. Additionally, you receive the following error message:

This problem occurs if the following conditions are true:

• Communicator 2005 sends the second message after Communicator 2005 receives a "200 Ok" response for the first message from the recipient
• Communicator 2005 sends the second message before Communicator 2005 sends an "ACK" acknowledgement message to the recipient.

In this situation, the recipient's Communicator 2005 rejects the second message.

How to obtain the hotfix

This issue is fixed in the Communicator 2005 Hotfix Package that is dated June 29, 2007. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

To work around this issue, configure Communicator 2005 to use the Transport Layer Security (TLS) transport.

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