CommandBook errors on load

gistfile1.txt

2012-03-04 17:17:57 [SEVERE] Could not load 'plugins/CommandSigns.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.NoClassDefFoundError: org/bukkit/event/player/PlayerListener
	at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:148)
	at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:290)
	at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:214)
	at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:207)
	at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:183)
	at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigurationManager.java:53)
	at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:163)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:490)
Caused by: java.lang.NoClassDefFoundError: org/bukkit/event/player/PlayerListener
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
	at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	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(ClassLoader.java:423)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
	at com.hans.CommandSigns.CommandSigns.<init>(CommandSigns.java:28)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
	at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:144)
	... 8 more
Caused by: java.lang.ClassNotFoundException: org.bukkit.event.player.PlayerListener
	at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
	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(ClassLoader.java:423)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
	... 27 more