Msn won’t sign me in

I work in msn many hours per day but in previous days there was a problem that msn won't sign me in. msn Says something like it can't get past a firewall blocking it and also can't get past a Proxy server.
So please anyone tell me what is the problem and how to fix

MSN Messenger
We could not sign you in to MSN Messenger. It appears you are behind a firewall that does not allow a direct connection to the Internet. We tried to sign you in through an HTTP proxy, but your Internet Explorer proxy settings are either missing or incorrect.
To adjust your IE proxy settings click the IE Tools menu click Internet Options click the Connection tab and then click LAN Settings.
