Hello. Me and my friends have made countless servers never having any issues other than in the beginning. But after we got it to work it has always just been: Click on the server jar, boom everyone can join. So, what had happened was my friend wanted to go back and play Minecraft 1.7.3 before the game was "ruined" as he called it (I disagree with him but thats not the point) so I got the server jar, started it up, and he couldn't join. No amount of changing settings, properties, or restarting the server would work. So, after a while, we decided to play normal 1.4.5 Minecraft. The exact same thing happened. Help would be much appreciated. We are using hamachi but have had no issues with hamachi before. Thanks in advance!
P.S. In case you didn't read the title i'm on a mac!