This event may be logged and the Firewall Service may have shut down when running ISA 2004/2006 because of a corruption in the Web Proxy log files. If the "Referring Server" field contains more data than the field can hold, then the log file will become corrupt and the Logging service will stop. You can fix this by removing the "Referring Server" field in the Web Proxy logging options.
for details on fixing this problem.
Information from Microsoft ISA Server Help Files: "The server failed to find the correct location for logging information. This information may be missing or incorrect. Open ISA Management and check the log properties to verify that file information is correct in the corresponding logging service. To do this, in the ISA Management console tree, click Servers and Arrays, click Name, click Monitoring Configuration, and then click Logs. Check the property sheet where logging is enabled for this service."