Calendar items delayed in Exchange 2003

I noticed that if you send a calendar item or update to a user from an Exchange 2003 server to someone with an Exchange 2007 server you may get a message delayed error or it will fail. Sometimes you get the error but the message goes through. All very strange. It has to do with 2007's inability to deal with 2003's message headers. A hot fix from Microsoft fixed us right up however.
Here is the URL to the article:
http://support.microsoft.com/kb/938650