Outlook 2007 does not open some calendar items that are sent from a non-Exchange mail server to an Exchange mail server

When a counter proposal message that uses iCalendar format is sent from a mail server that is not running Microsoft Exchange to a server that is running Exchange Server 2007, the recipient on the Exchange Server 2007 computer receives the following error message when the recipient tries to open the message in Microsoft Office Outlook 2007:Note A counter proposal message is a response for a meeting request. The counter proposal message is typically used when you have tentatively accepted a meeting, and you want to propose a new time for a meeting request.

The non-Exchange mail system does not provide some Exchange-specific properties in the header of a counter proposal message, such as the start time or the end time. However, Exchange Server 2007 relies on these properties. If these properties are not available, the Exchange server displays the message incorrectly. Therefore, Outlook cannot open the message.

To resolve this problem, install Update Rollup 5 for Exchange 2007 Service Pack 1.

For more information about Update Rollup 5 for Exchange 2007 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about Exchange iCalendar standards compliance, visit the following Microsoft Developer Network (MSDN) Web site:

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