Shoutbox

I think this is are problem with norton antivirus.   
Norton Antivirus added a new instant messaging scanning feature which can conflict with MSN Messenger. 

Open Norton Antivirus (Right-click on the Norton Antivirus icon in the System Tray/Notification Area (by the clock), choose'Open Norton Antivirus'), click Options, then Instant Messenger then uncheck MSN Instant Messenger or Windows Messenger click OK.

If you havent got norton then i don't know.