Bukkit

What steps will reproduce the problem?
1. Update scriptblock from 0.4.5 to 0.5.0
2. Reload plugins on the server

What is the expected output? What do you see instead?
2011-12-17 19:19:20 [SEVERE] Error occurred while enabling ScriptBlock v0.5.0 (Is it up to date?): net/milkbowl/vault/economy/Economy
java.lang.NoClassDefFoundError: net/milkbowl/vault/economy/Economy
    at fr.shereis.scriptblock.Main.onEnable(Main.java:85)
    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:188)
    at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:968)
    at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:280)
    at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:186)
    at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:169)
    at org.bukkit.craftbukkit.CraftServer.reload(CraftServer.java:436)
    at org.bukkit.Bukkit.reload(Bukkit.java:187)
    at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:22)
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:165)
    at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:378)
    at org.bukkit.craftbukkit.CraftServer.dispatchCommand(CraftServer.java:374)
    at net.minecraft.server.MinecraftServer.b(MinecraftServer.java:564)
    at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:541)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:425)
    at net.minecraft.server.ThreadServerApplication.run(SourceFile:457)
Caused by: java.lang.ClassNotFoundException: net.milkbowl.vault.economy.Economy
    at java.net.URLClassLoader$1.run(Unknown Source)
    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:36)
    at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:24)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 16 more

What version of the product are you using?
bukkit 1.0.1-R1
scriptblock 0.5.0
vault is not installed

it looks like that I forgot to make "Vault" Optional...

EDIT :

It looks like that I can't make Vault Optional, without major recoding...