Solved Slimefun java.lang.NoClassDefFoundError

Whenever I load up the Slimefun plugin on my server, I always get this error message:

[21:54:39 INFO]: [Slimefun] Enabling Slimefun v4.0.4
[21:54:39 INFO]: [Slimefun] Loading Files...
[21:54:39 INFO]: [Slimefun] Loading Config...
[21:54:39 INFO]: [Slimefun] Loading Items...
[21:54:40 INFO]: [ClearLag] No updates found!
[21:54:40 INFO]: [Slimefun] Loading Researches...
[21:54:40 INFO]: [Slimefun] Loading World Generators...
[21:54:40 ERROR]: Error occurred while enabling Slimefun v4.0.4 (Is it up to date?)
java.lang.NoClassDefFoundError: com/sk89q/worldedit/extent/Extent
at me.mrCookieSlime.Slimefun.SlimefunStartup.onEnable(SlimefunStartup.java:243) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:292) ~[craftbukkit.jar:git-Spigot-944aa20-420b983]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:340) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at org.bukkit.craftbukkit.v1_9_R1.CraftServer.loadPlugin(CraftServer.java:361) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at org.bukkit.craftbukkit.v1_9_R1.CraftServer.enablePlugins(CraftServer.java:321) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at net.minecraft.server.v1_9_R1.MinecraftServer.t(MinecraftServer.java:411) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at net.minecraft.server.v1_9_R1.MinecraftServer.l(MinecraftServer.java:376) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at net.minecraft.server.v1_9_R1.MinecraftServer.a(MinecraftServer.java:331) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at net.minecraft.server.v1_9_R1.DedicatedServer.init(DedicatedServer.java:269) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:527) [craftbukkit.jar:git-Spigot-944aa20-420b983]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_91]
Caused by: java.lang.ClassNotFoundException: com.sk89q.worldedit.extent.Extent
at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.8.0_91]
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:101) ~[craftbukkit.jar:git-Spigot-944aa20-420b983]
at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:86) ~[craftbukkit.jar:git-Spigot-944aa20-420b983]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_91]
at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.8.0_91]
... 12 more

I have already tried searching the error, messing around with the .class files, all to no avail. Anyone know what I can do to fix this? I have contacted the developer, but he seems to either be very busy at the moment, or simply not care about any issues people have. From what people have told me about him though, I would assume the 2nd reason is the answer.

 

@ItsFreakinHarry

This is a problem with WorldEdit. Make sure you have the most up to date WorldEdit installed on your server

 

Thanks for the help, fixed the issue

 

@ItsFreakinHarry
Mark this thread as solved if your problem has been solved.