http://blogs.technet.com/yuridiogenes/archive/2009/06/26/isa-server-support-life-cycle.aspxLately we had received some calls where ISA Server was not using the latest updates, which is fine although is not recommended. However when the subject is Service Pack then it might be a supportability blocker if ISA Server is not running within theen-USCommunityServer 2.1 SP1 (Build: 61025.2)