Did you make the time honored SNAFU and install your ISA firewall array in a workgroup configuration (bad idea) but install the CSS on a domain member (good idea)? If so, you probably ran into some problems with upgrading to the ISA firewall’s Service Pack 2.
If the Error 1603: Setup failed while registering new events and alerts. Refer to the KB article of this update for support error is driving you nuts, then head on over to https://blogs.technet.com/isablog/archive/2006/03/19/422473.aspx to solve the problem.
Thomas W Shinder, M.D.
MVP -- ISA Firewalls