Well, to begin with, your console log and the server's console log would be super, so we could see at least what causes the crash :3
Here is my game's log. Just follow the link.
http://pastebin.com/PunsTd6p
Server log, tell me if this is enough 11.06 14:32:47 [Server] INFO Unloading Player: rockstar_me1
11.06 14:32:47 [Disconnect] User rockstar_me1 has disconnected, reason: disconnect.genericReason
11.06 14:32:47 [Server] INFO at ch.run(SourceFile:93)
11.06 14:32:47 [Server] INFO at cg.c(TcpConnection.java:544)
11.06 14:32:47 [Server] INFO at cg.i(TcpConnection.java:324)
11.06 14:32:47 [Server] INFO at ef.a(Packet.java:142)
11.06 14:32:47 [Server] INFO at java.io.FilterInputStream.read(Unknown Source)
11.06 14:32:47 [Server] INFO at org.bouncycastle.crypto.io.CipherInputStream.read(Unknown Source)
11.06 14:32:47 [Server] INFO at org.bouncycastle.crypto.io.CipherInputStream.nextChunk(Unknown Source)
11.06 14:32:47 [Server] INFO at java.io.FilterInputStream.read(Unknown Source)
11.06 14:32:47 [Server] INFO at java.net.SocketInputStream.read(Unknown Source)
11.06 14:32:47 [Server] INFO at java.net.SocketInputStream.read(Unknown Source)
11.06 14:32:47 [Server] INFO at java.net.SocketInputStream.socketRead0(Native Method)
11.06 14:32:47 [Server] INFO java.net.SocketTimeoutException: Read timed out
11.06 14:32:15 [Server] INFO Turned on world auto-saving
11.06 14:32:15 [Multicraft] Backup done 0
11.06 14:32:10 [Server] INFO [1.4.7v5] Recieved client info from rockstar_me1
11.06 14:32:09 [Server] INFO Sending serverside check to: rockstar_me1
11.06 14:32:09 [Server] INFO Loading Player: rockstar_me1
11.06 14:32:08 [Multicraft] rockstar_me1 ran command Message of the Day
Oh, and my friend can get into the server perfectly. I made sure to ask him that first thing when this started happening.