One of my recent projects was documenting the migration of LCS 2005 with SP1 to OCS 2007 R2.

Should you be performing, or planning that migraton, you may appreciate the following list of prerequisites you will need on all of your LCS 2005 with SP1 servers. I also suggest you read the supporting information on these updates and hotfixes.

Ensure that Live Communications Server 2005 servers are patched with the following updates:

Live Communications Server Service Pack 1: This upgrade to the base LCS 2005 is available at http://www.microsoft.com/downloads/details.aspx?FamilyID=3508860C-2616-4B5A-BA00-353BE599A7B1&displaylang=en

Update for Live Communications Server 2005; February 10, 2006, available at http://support.microsoft.com/kb/911996

Live Communications Server 2005 post-Service Pack1 hotfix package: July 21, 2006, available at http://support.microsoft.com/kb/921543

Update for Live Communications Server 2005 Service Pack 1: September 2008 available at http://support.microsoft.com/kb/950614

Update your Communicator 2005 clients with the Communicator 2005 hotfix package: December 19, 2008 available at http://support.microsoft.com/kb/949280

For more information, please see the migration guide located here.

Enjoy!