Player connection problem

Hey! One of my players is having a serious problem when playing on my server. When he joins the server, he gets an EoS after two to thirty minutes. This is the console error:

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2011-07-20 14:00:02 [INFO] [Staff] riceman11 has joined the channel
2011-07-20 14:25:39 [SEVERE] java.net.SocketException: Socket closed
2011-07-20 14:25:39 [INFO] Connection reset
2011-07-20 14:25:39 [INFO] riceman11 lost connection: disconnect.quitting
2011-07-20 14:25:39 [SEVERE] at java.net.SocketOutputStream.socketWrite(Unknown Source)
2011-07-20 14:25:39 [SEVERE] at java.net.SocketOutputStream.write(Unknown Source)
2011-07-20 14:25:39 [SEVERE] at java.io.BufferedOutputStream.flushBuffer(Unknown Source)
2011-07-20 14:25:39 [SEVERE] at java.io.BufferedOutputStream.flush(Unknown Source)
2011-07-20 14:25:39 [SEVERE] at java.io.DataOutputStream.flush(Unknown Source)
2011-07-20 14:25:39 [INFO] [Staff] riceman11 has left the channel
2011-07-20 14:25:39 [SEVERE] at net.minecraft.server.NetworkWriterThread.run(SourceFile:116)

As far as I've seen, he and one other person is the only ones getting this error.

Any ideas how I might get rid of this?