Ah ha, I've run into this issue before and it really pisses me off when I need to go on for clan stuff. Simply restart your computer, and reload tremulous, also might work better if you start up your computer, log into your account, and wait like 15 minutes than try an load the game.
Does it freeze on a white screen? If it does try this, it will eventually work. Or you could just reinstall by downloading a new set of files... My way should definitely work