You are unable to read/review Encrypted e-mail messages for 24 hours after receipt

Note: This article discusses an issue that has recently been observed by Microsoft. 
The third-party products that are discussed in this article are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, regarding the performance or reliability of these products.

When you receive an encrypted e-mail message, you are unable to open (read) the message until 24 hours after the message has arrived.   You receive the following error when you attempt to open the message:

Cannot open this item.  Unknown Error.

This may not occur with every message, and may appear to be random.  This problem can occur when using Microsoft Outlook withg RPC or Outlook Anywhere, POP3 or IMAP4 for delivery, or when using Outlook Web Access (OWA).  The problem can also occur when you move messages from the Inbox to another mailbox folder. 

For information on servicing Exchange Server 2007 computers, see the following topic from Microsoft TechNet online:

Exchange 2007 Servicing
http://technet.microsoft.com/en-us/library/dd421853(EXCHG.80).aspx

A common element observed in these issues is that Trend Micro SMEX version 8 or 10 has been installed on Mailbox servers running Exchange Server 2007 Service Pack 1 Rollup Update 4 through Rollup Update 9. 

In reproduction testing, stopping Trend Micro services on the impacted Mailbox server allowed the messages to be read immediately.  This is not a recommended resolution.

This article will be updated with additional information as it becomes available.