Bukkit

What steps will reproduce the problem?
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1. STRANGE STUFF ON CONSOLE (CONSOLE STUFF DOWN BELOW)
2. /SW SETLOBBY
3.PRESSURE PLATE NOT WORING.
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What is the expected output? What do you see instead?
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I SHOULD SEE THE PRESSURE PLATE WORKING, AND TELEPORTING ME TO THE BECON, AND NO PROBLEM IN THE CONSOLE.
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What version of the product are you using?

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LATEST VERSION OF SKYWARS; CRAFTBUKKIT IS 1.7.9
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Do you have an error log of what happened?

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YES, HERE'S WHAT IT APPEARS ON THE CONSOLE:
[17:46:42 INFO]: [SkyWars] [ChestController] Registered 1 chest items ...
[17:46:42 ERROR]: Error occurred while enabling SkyWars v1.0.5 (Is it up to date?)
java.lang.NoClassDefFoundError: net/ess3/api/IEssentials
    at vc.pvp.skywars.utilities.ItemUtils.parseItem(ItemUtils.java:43) ~[?:?]
    at vc.pvp.skywars.controllers.KitController$Kit.<init>(KitController.java:193) ~[?:?]
    at vc.pvp.skywars.controllers.KitController.load(KitController.java:64) ~[?:?]
    at vc.pvp.skywars.controllers.KitController.<init>(KitController.java:34) ~[?:?]
    at vc.pvp.skywars.controllers.KitController.get(KitController.java:256) ~[?:?]
    at vc.pvp.skywars.SkyWars.onEnable(SkyWars.java:115) ~[?:?]
    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:250) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:324) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:404) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at org.bukkit.craftbukkit.v1_7_R3.CraftServer.loadPlugin(CraftServer.java:448) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at org.bukkit.craftbukkit.v1_7_R3.CraftServer.enablePlugins(CraftServer.java:382) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.MinecraftServer.n(MinecraftServer.java:352) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.MinecraftServer.g(MinecraftServer.java:326) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.MinecraftServer.a(MinecraftServer.java:282) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.DedicatedServer.init(DedicatedServer.java:182) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.MinecraftServer.run(MinecraftServer.java:436) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at net.minecraft.server.v1_7_R3.ThreadServerApplication.run(SourceFile:628) [craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
Caused by: java.lang.ClassNotFoundException: net.ess3.api.IEssentials
    at java.net.URLClassLoader$1.run(URLClassLoader.java:366) ~[?:1.7.0_55]
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355) ~[?:1.7.0_55]
    at java.security.AccessController.doPrivileged(Native Method) ~[?:1.7.0_55]
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354) ~[?:1.7.0_55]
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:77) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:62) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.3-59-g6efeddf-b3074jnks]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:425) ~[?:1.7.0_55]
    at java.lang.ClassLoader.loadClass(ClassLoader.java:358) ~[?:1.7.0_55]
    ... 17 more
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Please provide any additional information below.
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I ALREADY SETD UP THE MAP, AND ALREADY LOADED THE WORLD AND PLAYERS.
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I hope you could fix my problem, thanks!