Cosaly

I installed this Modpack: http://www.technicpack.net/modpack/novus-official-youtube-pack.895793 on my Server to play with my friends. And now the problem: When I join the nether, the server stopps and minecraft is closing. When I start the Server and Minecraft again, I cant join the Server, but my buddy can. It´s also very strange, that i already was in the Nether without any problems, but i tried again and then it happened. I had this problem before also, but then I just reset the server, because I didn´t play much. Here´s the log from the console: http://pastebin.com/xn6f7q2W I hope you can help me!