That's odd, the master server should be up currently as far as I know. Is your server filter setting set to "Internet"?
However, an alternative way to connect is to go to
Movie Battles II Server List and copy the IP to your clipboard, open up MB2, bring down console by pressing Shift + tilde (~ or `) and connect via typing /connect <IP> (without the <>). Alternatively you can try to set up the MB2Connect thing the web page points to in the bottom right corner.
If you're unable to connect this way too it could be a firewall or a version issue.