Falling through world in Multiplayer

I started up a Minecraft Server for me and my friend for the recent update, after a brief hiatus from multiplayer together. We have had it working perfectly before. I use Hamachi to create a network between us, and we have played on other games and maintain skype calls without any issues so the internet connection does not seem to be the issue. As soon as he joins the game, he is just falling through the world, even when teleported to me. I am not affected. After a while is he disconnected from the game.