not sure...

11.07 02:59:39 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)
11.07 02:59:39 [Server] INFO at java.lang.reflect.Method.invoke(Method.java:601)
11.07 02:59:39 [Server] INFO at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
11.07 02:59:39 [Server] INFO at sun.reflect.GeneratedMethodAccessor226.invoke(Unknown Source)
11.07 02:59:39 [Server] INFO at com.turt2live.antishare.ASListener.onEntityInteract(ASListener.java:1037)
11.07 02:59:39 [Server] INFO at com.turt2live.antishare.util.Messages.notifyParties(Messages.java:144)
11.07 02:59:39 [Server] INFO Caused by: java.lang.IllegalArgumentException: Null arguments are not allowed
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.ThreadServerApplication.run(SourceFile:582)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.MinecraftServer.run(MinecraftServer.java:413)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.MinecraftServer.s(MinecraftServer.java:481)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.DedicatedServer.t(DedicatedServer.java:239)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.MinecraftServer.t(MinecraftServer.java:592)
11.07 02:59:39 [Server] INFO at org.spigotmc.netty.NettyServerConnection.b(NettyServerConnection.java:125)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.ServerConnection.b(SourceFile:37)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.PlayerConnection.e(PlayerConnection.java:118)
11.07 02:59:39 [Server] INFO at org.spigotmc.netty.NettyNetworkManager.b(NettyNetworkManager.java:235)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.Packet7UseEntity.handle(SourceFile:36)
11.07 02:59:39 [Server] INFO at net.minecraft.server.v1_6_R2.PlayerConnection.a(PlayerConnection.java:1114)
11.07 02:59:39 [Server] INFO at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:463)
11.07 02:59:39 [Server] INFO at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:478)
11.07 02:59:39 [Server] INFO at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:30)
11.07 02:59:39 [Server] INFO at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
11.07 02:59:39 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
11.07 02:59:39 [Server] INFO org.bukkit.event.EventException
11.07 02:59:39 [Server] SEVERE Could not pass event PlayerInteractEntityEvent to AntiShare v5.5.0-SNAPSHOT

Looks like the fix I made for horses broke because Bukkit fixed it.

Does build 458 work?

Fixed in build 458