For just under a year, the use of the URL http://www.ru.ac.za/proxy.pac for proxy auto-configuration has been deprecated in favour of a new URL, http://wpad.ru.ac.za/. Details of this change were September last year.
For the last few months, people who've still been using the old proxy.pac URL have been receiving an error message (ERR_OLD_PROXY_SETTINGS) asking them to reconfigure their web browsers. To date this error message has been advisory -- it'd allow normal access to the proxy servers after about thirty seconds, in the same way as high-traffic sites.
As of today, http://www.ru.ac.za/proxy.pac is no longer supported. The last few remaining users of this URL will now be unable to access the web. For the next month or so, they'll continue to see ERR_OLD_PROXY_SETTINGS but will not be able to access the web until they update their settings. Thereafter, the old proxy.pac configuration file will be removed.