I did a ggle search for you and came accross this page that might be of some use:
http://www.microsoft.com/communities/newsgroups/l...3-0d9dd7c28e88&p=1
On that page it said that some possible reasons behind it are that the messenger server is curently unavaliable or that you might be behind some kind of firewall that is restricting your access to messenger. Still it might be wise to have a look for yourself nd a more detailed google search too.