When you start Microsoft Office Communicator 2007 R2, you receive the following error message:
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.
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.
To resolve this problem, apply the following update:
969695 Description of the Communicator 2007 R2 hotfix rollup package: June 2009
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.