The full message is:

The system security configuration application failed. For more information, view the log file, Securewiz.log, located in the ISA Server installation folder.

If your Windows Server 2003 computer is NOT joined to a domain, you will experience this problem.

NOTE: The ISA Server Security Configuration Wizard ran the following command:

Secedit /configure /DB "c:\tmp\secedit\sdb11.sdb" /verbose /log "c:\tmp\secedit\1.log" /CFG "c:\tmp\secedit\inf12.tmp"
where the Inf12.tmp file is based upon the Hisecws.inf security template, which requires a domain account.

You can either join the ISA server computer to a domain, or select the Secure Security Level, which may not be appropriate for your environment.

NOTE: See http://www.microsoft.com/isaserver/setupserver2003.asp.