Server is kicking me when i enter nether.

Code:

2011-10-20 21:07:36 [INFO] Jareq [/91.224.104.28:3697] logged in with entity id 86 at ([world_nether] -27.5, 78.0, 43.5)
2011-10-20 21:07:37 [SEVERE] java.net.SocketException: Socket closed
2011-10-20 21:07:37 [INFO] Connection reset
2011-10-20 21:07:37 [SEVERE]    at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:99)
2011-10-20 21:07:37 [SEVERE]    at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
2011-10-20 21:07:37 [SEVERE]    at java.io.BufferedOutputStream.flushBuffer(BufferedOutputStream.java:65)
2011-10-20 21:07:37 [SEVERE]    at java.io.BufferedOutputStream.flush(BufferedOutputStream.java:123)
2011-10-20 21:07:37 [SEVERE]    at java.io.DataOutputStream.flush(DataOutputStream.java:106)
2011-10-20 21:07:37 [SEVERE]    at net.minecraft.server.NetworkWriterThread.run(SourceFile:104)
2011-10-20 21:07:37 [INFO] Jareq lost connection: disconnect.overflow

So, i wrote /world command, i switched the world to nether and it kick's me out.

 

Could you give us the full serverlog and heck, the serverconfig?
What plugins are you using?
What version of bukkit are you running?