Here are the latest KB articles for Office Communicator 2007 and Office Communicator 2005:

http://support.microsoft.com/?kbid=944686
Description of the Communicator 2007 hotfix package: November 6, 2007
11/9/2007
Windows NT
Office Communicator 2007 EN
EN-US

http://support.microsoft.com/?kbid=944687
Error message when you try to change an IM conversation into a multiparty conference in Communicator 2007: "Your attempt to start a conference was unsuccessful."
11/9/2007
Windows NT
Office Communicator 2007 EN
EN-US

http://support.microsoft.com/?kbid=944612
Error message when you try to start a meeting in Communicator 2005: “Microsoft Office Live meeting could not be started. Please make sure that the latest version of the program is installed and properly configured"
11/19/2007
Windows NT
Office Communicator 2005 EN
EN-US

- Michael Platts

  Support Escalation Engineer