The link above references Norton as the possible cause, but does not link you to the Norton Removal Tool
which would remove Norton from the system. If the issue persists after that, then we can chenc for proxies in your internet browsers.
Lets check for Proxies now before removal of Norton.
Go to Control Panel then Internet Options > Connection Tab > LAN Settings nothing should be checked.
In Firefox go to Tools > Options > Advanced > Network Tab > Settings No Proxies should be set up.