Sometimes. I ran into it mostly with everybuddy. I am no MSN guru, but I think they change their servers around sometimes to "foil" the non MSN messengers supporting their service. Best thing to do, change messengers
Or, see if there is an update, or see if there is a way to find the "new" name of the server, and add it into GAIM's server part. I have to do that for Yahoo! every so often too.