I assume you're using a Hotmail account? That error message is something
saying that Outlook has sent a bad request. Generally, this comes from a
proxy server or firewall that doesn't understand the HTTP/DAV protocol that
is used to talk to Hotmail. I'd say that someone (either your ISP or your
network administrator) recently installed or reconfigured a proxy server
between you and the Internet. Contact the proper person and ask them to
either upgrade or reconfigure in order to support HTTP/DAV.