I have a server and I use citizens 1.2 but every time I stop the server when I start it back up all the NPC's I made are gone, they're still in the file though, and also they won't talk to people even when I set them to. Also when I start the server it says:

[SEVERE] Error occurred while enabling Citizens v1.2 (Is it up to date?)
java.lang.NoClassDefFoundError: net/milkbowl/vault/economy/Economy
at net.citizensnpcs.Economy.init(Economy.java:21)
at net.citizensnpcs.Citizens.onEnable(Citizens.java:122)
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:215)
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337)
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:381)
at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:256)
at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:238)
at net.minecraft.server.MinecraftServer.t(MinecraftServer.java:381)
at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:368)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:197)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.ClassNotFoundException: net.milkbowl.vault.economy.Economy
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:41)
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:29)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 12 more

*EDIT
The plug-in's I have are:

SetRankPB, Citizens, Punishmental, GroupManager, WorldEdit, Build-A-Mob, iConomy, BookWorm, Pigasus, BKCommonLib, ClearLag, MobDisguise, MobArena, Essentials, EssentialsProtect, EssentialsSpawn, NoLagg, EssentialsChat, Factions.