http://blogs.technet.com/isablog/archive/2008/07/21/64-bit-rpc-traffic-fails-across-isa-sever-2006.aspx1. Introduction This post describes an issue where two 64-bit Windows hosts are failing to communicate to each other using RPC . The hosts each operate in a network physically separated from each other by ISA Server 2006. Figure 1 illustrates the basicen-USCommunityServer 2.1 SP1 (Build: 61025.2)