[14:40:39] [Server thread/ERROR]: Uh oh! You've found an error in Core.
This is an error caused while running your code, so you may be able to find a workaround, but is ultimately an error in Core itself.
The line of code that caused the error was this:
@hat = 'd93e9067-b5c9-485c-b249-d67ff01a6953'
set_entity_rider(@hat, '7c15299a-c58a-4577-9da2-0a8b5c045280')
on or around /minecraft/hub/plugins/CommandHelper/LocalPackages/playerrider.ms:9.
Please report this error to the developers, and be sure to include the version numbers:
Server version: 1.9.2-R0.1-SNAPSHOT;
CommandHelper version: 3.3.2-SNAPSHOT.3107-;
Loaded extensions and versions:
Core (version 3.3.2);
CHSpigot (version 1.5.0);
Here's the stacktrace:
java.lang.IllegalStateException: Circular entity riding! EntitySlime['Slime'/6427, l='hub', x=19.88, y=62.06, z=-12.01] EntityPlayer['Altaleb'/5184, l='hub', x=20.50, y=62.06, z=-12.50](Altaleb at 20.5,62.0625,-12.5)
    at com.google.common.base.Preconditions.checkState(Preconditions.java:200)
    at net.minecraft.server.v1_9_R1.Entity.o(Entity.java:1693)
    at net.minecraft.server.v1_9_R1.Entity.a(Entity.java:1662)
    at net.minecraft.server.v1_9_R1.EntityPlayer.a(EntityPlayer.java:618)
    at net.minecraft.server.v1_9_R1.Entity.startRiding(Entity.java:1650)
    at org.bukkit.craftbukkit.v1_9_R1.entity.CraftEntity.setPassenger(CraftEntity.java:322)
    at com.laytonsmith.abstraction.bukkit.entities.BukkitMCEntity.setPassenger(BukkitMCEntity.java:230)
    at com.laytonsmith.core.functions.EntityManagement$set_entity_rider.exec(EntityManagement.java:1677)
    at com.laytonsmith.core.Script.eval(Script.java:375)
    at com.laytonsmith.core.Procedure.execute(Procedure.java:218)
    at com.laytonsmith.core.Procedure.cexecute(Procedure.java:168)
    at com.laytonsmith.core.Script.eval(Script.java:304)
    at com.laytonsmith.core.functions.Exceptions$_try.execs(Exceptions.java:172)
    at com.laytonsmith.core.Script.eval(Script.java:334)
    at com.laytonsmith.core.Script.eval(Script.java:344)
    at com.laytonsmith.core.Script.seval(Script.java:253)
    at com.laytonsmith.core.functions.BasicLogic$_if.execs(BasicLogic.java:85)
    at com.laytonsmith.core.Script.eval(Script.java:334)
    at com.laytonsmith.core.Script.eval(Script.java:344)
    at com.laytonsmith.core.MethodScriptCompiler.execute(MethodScriptCompiler.java:1977)
    at com.laytonsmith.core.MethodScriptCompiler.execute(MethodScriptCompiler.java:1934)
    at com.laytonsmith.core.events.AbstractEvent.execute(AbstractEvent.java:109)
    at com.laytonsmith.core.events.BoundEvent.execute(BoundEvent.java:320)
    at com.laytonsmith.core.events.BoundEvent.trigger(BoundEvent.java:278)
    at com.laytonsmith.core.events.EventUtils.FireListeners(EventUtils.java:253)
    at com.laytonsmith.core.events.EventUtils.TriggerListener(EventUtils.java:240)
    at com.laytonsmith.abstraction.bukkit.events.drivers.BukkitEntityListener.onClickEnt(BukkitEntityListener.java:48)
    at sun.reflect.GeneratedMethodAccessor48.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.laytonsmith.commandhelper.CommandHelperPlugin$8.execute(CommandHelperPlugin.java:509)
    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
    at org.bukkit.plugin.TimedRegisteredListener.callEvent(TimedRegisteredListener.java:36)
    at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:517)
    at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:502)
    at net.minecraft.server.v1_9_R1.PlayerConnection.a(PlayerConnection.java:1570)
    at net.minecraft.server.v1_9_R1.PacketPlayInUseEntity.a(PacketPlayInUseEntity.java:48)
    at net.minecraft.server.v1_9_R1.PacketPlayInUseEntity.a(PacketPlayInUseEntity.java:5)
    at net.minecraft.server.v1_9_R1.PlayerConnectionUtils$1.run(SourceFile:13)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:45)
    at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:811)
    at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:404)
    at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:721)
    at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:620)
    at java.lang.Thread.run(Thread.java:745)