http://blogs.msdn.com/velocity/archive/2009/06/22/troubleshooting-velocity-series-ii.aspxHow to ensure you have correct client libraries This section is more important for people who are upgrading from CTP2 to CTP3. Since Microsoft project code named “Velocity” bits are not backward compatible, while upgrading the cache hosts, “Velocity”en-USCommunityServer 2.1 SP1 (Build: 61025.2)