LAN Problem when a player joins

[KoalaKonundrum]

Everytime I open my Big Dig game to LAN and a player joins, a problem occurs. The game does not crash and I can play it perfectly on singleplayer or on LAN without another connected. All of the mobs freeze and you cannot open any chests or use anything at all. Right clicking a crafting table, for example, does not open the GUI. The player that joined cannot move off of the block he/she originally spawned on or else he/she will fall endlessly. To me, the joined player appears to be completely frozen in the spot. I tested using LAN on Big Dig with other saves and the result is not duplicated and it works perfectly. It is only on that specific map that it does this. I hope someone has at least seen this before and, better yet, has a solution. If their is some kind of log available, I will search for it, but since it did not crash there isn't a crash log. Is there a saved log of every time the game is played or just when crashes occur? Anyways, I hope someone has a solution, because I have worked very hard on this world and I don't want to lose it! Thanks in advance.