my friends crash when they go on my server

[Ilikepie101]

Launcher/Pack Version: Tekkit (1.0.1.3)

Operating System: Windows 7 Home Premium

Version of Java: Java 7 Update 4

Problem: My server always run perfectly for me, but for my brother he gets on and eventually gets disconnected. This is the error message:

17:16:48 [iNFO] Connection reset

17:16:48 [iNFO] cubsfanmikey lost connection: disconnect.quitting

17:16:48 [sEVERE] java.net.SocketException: Socket closed

17:16:48 [sEVERE] at java.net.SocketOutputStream.socketWrite(Unknown Sourc

e)

17:16:48 [sEVERE] at java.net.SocketOutputStream.write(Unknown Source)

17:16:48 [sEVERE] at java.io.BufferedOutputStream.flushBuffer(Unknown Sour

ce)

17:16:48 [sEVERE] at java.io.BufferedOutputStream.flush(Unknown Source)

17:16:48 [sEVERE] at java.io.DataOutputStream.flush(Unknown Source)

17:16:48 [sEVERE] at net.minecraft.server.NetworkWriterThread.run(SourceFi

le:103)

17:16:52 [iNFO] cubsfanmikey [/192.168.2.7:61401] logged in with entity id 1190

at ([world] 205.3125, 64.0, 326.28125)

17:16:52 [sEVERE] java.net.SocketException: Socket closed

17:16:52 [sEVERE] at java.net.SocketOutputStream.socketWrite(Unknown Sourc

e)

17:16:52 [sEVERE] at java.net.SocketOutputStream.write(Unknown Source)

17:16:52 [sEVERE] at java.io.BufferedOutputStream.flushBuffer(Unknown Sour

ce)

17:16:52 [sEVERE] at java.io.BufferedOutputStream.flush(Unknown Source)

17:16:52 [sEVERE] at java.io.DataOutputStream.flush(Unknown Source)

17:16:52 [sEVERE] at net.minecraft.server.NetworkWriterThread.run(SourceFi

le:103)

17:16:52 [iNFO] cubsfanmikey lost connection: disconnect.endOfStream

It happens every time he tries to log on!

He has the same version of Java, Windows 7 Ultimate, and we are using the same internet. He starts lagging like he cant open anything, like chests or crafting tables.

I have a regular server and it does the same thing. But when i try to have one of my friends on their own computer, it works fine for them.

[Torezu]

Socket Exceptions are usually caused by a firewall or AV, or a lack of port-forwarding. It's also possible there's a duck in your server.

[Ilikepie101]

I think I port forwarded fine because my friends could get on it from far away. i turned my windows firewall off, but it keeps happening. We are the only ones that ever go on. how do i fix the duck thing.