getting this error when login out of the current build of 1.5.1 #2730
I did some digging the get broken on build #2723 when this is changed:

Throw exception for disabled plugin tasks. Fixes BUKKIT-3951

that's all that was changed in that build and it broke the plugin on server shut down.

10:30:22 AM [SEVERE] Could not pass event PluginDisableEvent to Vault v1.2.24-b304
org.bukkit.event.EventException
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:427)
at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:477)
at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:462)
at org.bukkit.plugin.java.JavaPluginLoader.disablePlugin(JavaPluginLoader.java:475)
at org.bukkit.plugin.SimplePluginManager.disablePlugin(SimplePluginManager.java:400)
at org.bukkit.plugin.SimplePluginManager.disablePlugins(SimplePluginManager.java:393)
at org.bukkit.craftbukkit.v1_5_R2.CraftServer.disablePlugins(CraftServer.java:277)
at net.minecraft.server.v1_5_R2.MinecraftServer.stop(MinecraftServer.java:331)
at net.minecraft.server.v1_5_R2.MinecraftServer.run(MinecraftServer.java:438)
at net.minecraft.server.v1_5_R2.ThreadServerApplication.run(SourceFile:573)
Caused by: org.bukkit.plugin.IllegalPluginAccessException: Plugin attempted to register task while disabled
at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftScheduler.validate(CraftScheduler.java:394)
at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftScheduler.runTaskTimerAsynchronously(CraftScheduler.java:137)
at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftScheduler.scheduleAsyncRepeatingTask(CraftScheduler.java:133)
at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftScheduler.scheduleAsyncDelayedTask(CraftScheduler.java:108)
at com.alecgorge.minecraft.jsonapi.api.JSONAPIStream.pushMessage(JSONAPIStream.java:105)
at com.alecgorge.minecraft.jsonapi.api.JSONAPIStream.addMessage(JSONAPIStream.java:81)
at com.alecgorge.minecraft.jsonapi.JSONServer.logConsole(JSONServer.java:151)
at com.alecgorge.minecraft.jsonapi.streams.ConsoleHandler.publish(ConsoleHandler.java:31)
at java.util.logging.Logger.log(Unknown Source)
at java.util.logging.Logger.doLog(Unknown Source)
at java.util.logging.Logger.log(Unknown Source)
at java.util.logging.Logger.info(Unknown Source)
at net.milkbowl.vault.economy.plugins.Economy_Essentials$EconomyServerListener.onPluginDisable(Economy_Essentials.java:199)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:425)

This is a bukkit bug. There is no way to unregister events, and it seems the plugin handling doesn't do this in the backend properly, or for some reason the json handler is still running when the plugin disables. either way, this is not an issue with Vault, the line you posted about in Vault is a logger, it should log to console, but it appears you're attempting to use a plugin that handles logging outside of the normal means. This is what is causing the error.