Bukkit

What steps will reproduce the problem?
1. Have many players.
2. Jail 1 or more persons in another world then jail and wait for it if nothing happens.
3. Receive error when lucky.

What is the expected output? What do you see instead?
Normal behavior expected, server crash instead.

What version of the product are you using? Which version of Java are you running and which version of craftbukkit?
Swornjail v2.3
Craftbukkit v1.4.6 R0.3 beta

Do you have an error log of what happened?
Yes, from NoLagg (more info: http://dev.bukkit.org/server-mods/nolagg/pages/synchronized-code-access-nolagg/):
2013-01-15 17:09:23 [SEVERE] java.lang.ArrayIndexOutOfBoundsException
2013-01-15 17:09:23 [SEVERE] Encountered an unexpected exception ArrayIndexOutOfBoundsException
java.lang.ArrayIndexOutOfBoundsException
2013-01-15 17:09:23 [WARNING] Could not properly handle event PLAYER_CHANGED_WORLD:
java.lang.IllegalAccessError: Synchronized code got accessed from another thread: com.minesworn.swornjail.threads.JailRelocateThread
at org.bukkit.event.NLTCListener.onPlayerChangedWorld(NLTCListener:0)
at sun.reflect.GeneratedMethodAccessor425.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at net.minecraft.server.v1_4_6.PlayerList.moveToWorld(PlayerList.java:415)
at org.bukkit.craftbukkit.v1_4_6.entity.CraftPlayer.teleport(CraftPlayer.java:392)
at org.bukkit.craftbukkit.v1_4_6.entity.CraftEntity.teleport(CraftEntity.java:189)
at com.minesworn.swornjail.threads.JailRelocateThread.run(JailRelocateThread.java:29)
2013-01-15 17:09:23 [INFO] This error is logged only once: it could have occurred multiple times by now.
2013-01-15 17:09:23 [INFO] Potential failures may occur in other plugins handling this Event.
2013-01-15 17:09:23 [INFO] Please contact one of the authors of plugin 'SwornJail': t7seven7t
2013-01-15 17:09:23 [SEVERE] This crash report has been saved to: /home/minecraft/Minecraft/./crash-reports/crash-2013-01-15_17.09.23-server.txt
2013-01-15 17:09:33 [INFO] Connection reset
2013-01-15 17:09:39 [WARNING] [Server] The main thread failed to respond after 10 seconds
2013-01-15 17:09:39 [WARNING] [Server] What follows is the stack trace of the main thread
2013-01-15 17:09:39 [WARNING] [Server] at java.lang.Thread.sleep(Native Method)
2013-01-15 17:09:39 [WARNING] [Server] at net.minecraft.server.v1_4_6.DedicatedServer.a(DedicatedServer.java:205)
2013-01-15 17:09:39 [WARNING] [Server] at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:455)
2013-01-15 17:09:39 [WARNING] [Server] at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
2013-01-15 17:09:45 [INFO] Connection reset
2013-01-15 17:09:51 [WARNING] [Server] The main thread is still stuck, current loop line is:
2013-01-15 17:09:51 [WARNING] [Server] at net.minecraft.server.v1_4_6.DedicatedServer.a(DedicatedServer.java:205)
2013-01-15 17:09:57 [INFO] Connection reset
2013-01-15 17:10:05 [INFO] Read timed out
2013-01-15 17:10:15 [INFO] Connection reset

Please provide any additional information below.
http://dev.bukkit.org/server-mods/nolagg/pages/synchronized-code-access-nolagg/

Maybe this information could help (source: http://dev.bukkit.org/server-mods/nolagg/)
Prevent cross-thread access for events

As it seems, some plugins don't follow the rules and use Bukkit methods in another thread. This plugin will notify you and cancel if possible whenever this happens so other plugins understand their mistake. If you encounter a lot of spam in the console, first check the stack trace for the plugin that caused the error. Report this error to the author or remove the plugin, if you have questions you are free to ask. Note: Bukkit add isSynchronous() to the event. A lot of plugins are, however, uninformed about this property. Until it is well-known, this feature will be in NoLagg.