18:07:36 [SEVERE] java.lang.ClassCastException: org.bukkit.craftbukkit.util.Stru
ctureGrowDelegate cannot be cast to net.minecraft.server.World
18:07:36 [SEVERE]       at net.minecraft.server.WorldGenForest.generate(WorldGen
Forest.java:49)
18:07:36 [SEVERE]       at net.minecraft.server.BlockSapling.grow(BlockSapling.j
ava:101)
18:07:36 [SEVERE]       at net.minecraft.server.BlockSapling.a(BlockSapling.java
:33)
18:07:36 [SEVERE]       at net.minecraft.server.World.l(World.java:2060)
18:07:36 [SEVERE]       at net.minecraft.server.World.doTick(World.java:1776)
18:07:36 [SEVERE]       at net.minecraft.server.MinecraftServer.w(MinecraftServe
r.java:567)
18:07:36 [SEVERE]       at net.minecraft.server.MinecraftServer.run(MinecraftSer
ver.java:470)
18:07:36 [SEVERE]       at net.minecraft.server.ThreadServerApplication.run(Sour
ceFile:492)
18:07:36 [SEVERE] Unexpected exception
java.lang.ClassCastException: org.bukkit.craftbukkit.util.StructureGrowDelegate
cannot be cast to net.minecraft.server.World
        at net.minecraft.server.WorldGenForest.generate(WorldGenForest.java:49)
        at net.minecraft.server.BlockSapling.grow(BlockSapling.java:101)
        at net.minecraft.server.BlockSapling.a(BlockSapling.java:33)
        at net.minecraft.server.World.l(World.java:2060)
        at net.minecraft.server.World.doTick(World.java:1776)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:567)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:470)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)