Error message when you send an instance message to a contact that is hosted on Communications Server 2007 in Communicator 2005 or in Communicator 2007: "This message was not delivered"

In Microsoft Office Communicator 2005 or in Microsoft Office Communicator 2007, you send an instance message to a contact that is hosted on Microsoft Office Communications Server 2007. When you do this, you may receive the following error message:

This problem occurs because a new encryption key may be corrupted when it is generated. This condition may occur if the first two encryption and decryption operations are performed at the same time. If the encryption key is corrupted, the decryption operations fail for security associations that are generated for all route sets during the lifetime of the key.

To resolve this problem, apply hotfix 949260.

For more information, click the following article number to view the article in the Microsoft Knowledge Base: Note This hotfix synchronizes the first call to the CryptEncrypt operation or to the CryptDecrypt operation.

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