From a newsgroup post: "By default, this service is not started in a standard SBS 2003 installation. If this service is started and it is not used by any client for 15 minutes, it will detect this and automatically stop. This event is logged as a result of this situation. If you are encountering these events, please feel free to stop this service, as it will not affect your basic functionalities.
You can disable the WinHTTP Web Proxy Auto-Discovery Service from the Services console:
1. Open the Server Management console.
2. Select Advanced Management -> Computer Management -> Services and
Applications -> Services.
3. Locate the service "WinHTTP Web Proxy Auto-Discovery Service", and open its properties.
4. Set it to "Disable" so this service will not run on next restart. You can click "Stop" to stop this service if it is running.
5. Click "OK" to take effect".
provides information on how to configure firewall and Web proxy client Autodiscovery in Windows Server 2003.
See the link to "WinHTTP AutoProxy Support" for an overview of AutoProxy.