If you using gnome, and turned off the proxy at the network level, you also need to make sure you don't have proxy enabled in your terminal
? gconftool-2 -a /system/http_proxy
host = http://localhost/
port = 2000
use_http_proxy = false
use_authentication = false
authentication_password =
authentication_user =
ignore_hosts = [localhost,127.0.0.0/8]
gconftool-2 -t string -s /system/http_proxy/host ""
gconftool-2 -u /system/http_proxy/port
gconftool-2 -u /system/http_proxy/host
unset http_proxy