I have one computer on a small Win Server 2003 network with Office 2007 on the clients that experiences this problem. Randomly, when a new message is opened Outlook presents an hour glass as if trying to open the note, and then closes Outlook. A second attempt after reopening Outlook is successful.
There does not seem to be any similarity among the messages, with or without attachments, etc. I removed Office 2007 on this computer and reinstalled it, but the issue persists.