Help server wont work right!!

i have a hamachi server and it worked fine last night with a guy now im trying to get my friends on and it worked both go on but i wanted to change the world so we could have fun and have a new one so i gointo properties change the name to another one i have but only one could get on when the other trie d to join it says"bad log in" i made a new world same thing same guy. i dont know what to do
also when he tries to join it says "[INFO] /<what i asume is an ip> lost connection" on the java serve