cauth error

09:57:46 [SEVERE] Could not load 'plugins\CAuth.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.NoClassDefFoundError: org/bu
kkit/util/config/Configuration
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:151)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:213)
        at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:189)
        at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigur
ationManager.java:53)
        at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:166)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.NoClassDefFoundError: org/bukkit/util/config/Configuration
        at csharp.cauth.CAuth.<clinit>(CAuth.java:57)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:140)
        ... 8 more
Caused by: java.lang.ClassNotFoundException: org.bukkit.util.config.Configuratio
n
        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