Safari Can't Connect To Localhost CUPS

I've recently upgraded a number of user computers running 10.4 and two computers, one intel, one PPC, are unable to connect to the localhost CUPS server. The error message is "Safari can't open the page "http://localhost:631/" because Safari can't connect to the server "localhost"". I have tried accessing the page via localhost:631 and 127.0.0.1:631 to no avail. System, httpd, and cups logs seem normal. Restarts and upgrades to Safari do not help. Using Firefox does not help. Nor does restarting the apachectl daemon. On top of all this, the localhost pings normally. Has anyone seen this before? Any ideas?