LogError5

04:11:06 [SEVERE] Error occurred while enabling NoCheatPlus v3.8.4-RC-b271 (Is it up to date?)
java.lang.NoClassDefFoundError: net/minecraft/server/IBlockAccess
	at fr.neatmonster.nocheatplus.NoCheatPlus.onEnable(NoCheatPlus.java:407)
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:217)
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:457)
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:381)
	at org.bukkit.craftbukkit.v1_4_6.CraftServer.loadPlugin(CraftServer.java:282)
	at org.bukkit.craftbukkit.v1_4_6.CraftServer.enablePlugins(CraftServer.java:264)
	at net.minecraft.server.v1_4_6.MinecraftServer.j(MinecraftServer.java:321)
	at net.minecraft.server.v1_4_6.MinecraftServer.e(MinecraftServer.java:300)
	at net.minecraft.server.v1_4_6.MinecraftServer.a(MinecraftServer.java:259)
	at net.minecraft.server.v1_4_6.DedicatedServer.init(DedicatedServer.java:149)
	at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:399)
	at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:849)
Caused by: java.lang.ClassNotFoundException: net.minecraft.server.IBlockAccess
	at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:70)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:53)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
	... 12 more