incorrect proxy setup in your system settings.
# In the Control Panel Home in Windows Vista, click Network and Internet and click Internet Options.
Alternately, in Control Panel in Windows XP and Classic View of Control Panel in Windows Vista, open Internet Options.
# In the resulting dialog, click the Connections tab, then click the LAN Settings button.
# In the Proxy Server section of the Local Area Network Settings window, verify that your proxy settings are correct. If they're not, correct them.
# If your settings are correct, try turning the proxy off for troubleshooting purposes. To do this, deselect the "Use a proxy server for your LAN" checkbox.
If you're not on Windows - ignore above.