Error

org.bukkit.command.CommandException: Unhandled exception executing command 'npc' in plugin Citizens v1.0.8
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:37)
	at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:85)
	at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:255)
	at net.minecraft.server.NetServerHandler.handleCommand(NetServerHandler.java:675)
	at net.minecraft.server.NetServerHandler.chat(NetServerHandler.java:638)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:632)
	at net.minecraft.server.Packet3Chat.a(Packet3Chat.java:32)
	at net.minecraft.server.NetworkManager.a(NetworkManager.java:195)
	at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:74)
	at net.minecraft.server.NetworkListenThread.a(SourceFile:100)
	at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:370)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:285)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:394)
Caused by: java.lang.NoClassDefFoundError: com/earth2me/essentials/api/Economy
	at com.nijikokun.register.payment.MethodEEco.hasAccount(MethodEEco.java:38)
	at com.fullwall.Citizens.Economy.ServerEconomyInterface.playerHasEnough(ServerEconomyInterface.java:25)
	at com.fullwall.Citizens.Economy.ServerEconomyInterface.hasEnough(ServerEconomyInterface.java:90)
	at com.fullwall.Citizens.Economy.EconomyHandler.canBuy(EconomyHandler.java:117)
	at com.fullwall.Citizens.CommandExecutors.BasicExecutor.onCommand(BasicExecutor.java:51)
	at org.bukkit.command.PluginCommand.execute(PluginCommand.java:35)
	... 12 more
Caused by: java.lang.ClassNotFoundException: com.earth2me.essentials.api.Economy
	at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:36)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:24)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:319)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:254)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:399)
	... 18 more
>