When you start Microsoft Office Communicator 2007 R2, you receive the following error message:
This problem occurs when Office Outlook is installed on a computer that is running an x64-based version of Windows 7 or Windows Server 2008.
Either there is no default mail client or the current mail client cannot fulfill the message request. Please run Microsoft Office Outlook and set it as the default mail client.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.