Microsoft Office Communicator 2007 could not retrieve calendar or Out of Office information from Exchange Web Services

If you upgrade your Exchange organization to Exchange 2010 (or greenfield installation), and your not patching your office communicator 2007 regulary, you may experience the following message :

Resolution for the problem can be found on the following Microsoft published article :
http://support.microsoft.com/kb/2028885 or http://support.microsoft.com/kb/2300255 .