Jellybeangod

Hello, Whenever I try to set up a Voltz server, no-one else can find or connect to it. I am using hamachi, and the people who are trying to connect are in the hamachi server. They have the correct IP, and the correct version of Voltz, but they still can't seem to find the server. The only things I changed in the config settings are the IP, the world name, and the motd. I am also having this exact same problem with tekkit. I don't know what else to do to fix it. Please help.