Can someone help me with this crash report

java.lang.NoClassDefFoundError: net/minecraft/world/World$2
at net.minecraft.world.World.func_147460_e(World.java:691)
at net.minecraft.world.World.func_147459_d(World.java:625)
at net.minecraft.world.World.func_147444_c(World.java:590)
at net.minecraft.world.World.func_147465_d(World.java:456)
at net.minecraft.block.BlockDynamicLiquid.func_149813_h(SourceFile:117)
at net.minecraft.block.BlockDynamicLiquid.func_149674_a(SourceFile:102)
at net.minecraft.world.WorldServer.func_147454_a(WorldServer.java:443)
at net.minecraft.world.WorldServer.func_147464_a(WorldServer.java:420)
at net.minecraft.block.BlockDynamicLiquid.func_149726_b(SourceFile:225)
at net.minecraft.world.chunk.Chunk.func_150807_a(Chunk.java:646)
at net.minecraft.world.World.func_147465_d(World.java:442)
at net.minecraft.block.BlockDynamicLiquid.func_149813_h(SourceFile:117)
at net.minecraft.block.BlockDynamicLiquid.func_149674_a(SourceFile:102)
at net.minecraft.world.gen.feature.WorldGenLiquids.func_76484_a(SourceFile:39)
at biomesoplenty.common.world.generation.ForcedWorldFeatureBOP.generate(ForcedWorldFeatureBOP.java:20)
at biomesoplenty.common.world.forcedgenerators.PondForcedGenerator.setupGeneration(PondForcedGenerator.java:32)
at biomesoplenty.common.world.decoration.BOPDecorationManager.generate(BOPDecorationManager.java:56)
at cpw.mods.fml.common.registry.GameRegistry.generateWorld(GameRegistry.java:102)
at net.minecraft.world.gen.ChunkProviderServer.func_73153_a(ChunkProviderServer.java:220)
at net.minecraft.world.chunk.Chunk.func_76624_a(Chunk.java:1046)
at net.minecraft.world.gen.ChunkProviderServer.func_73158_c(ChunkProviderServer.java:130)
at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:257)
at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:129)
at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:152)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:665)


A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- System Details --
Details:
Minecraft Version: 1.7.2
Operating System: Windows 8 (x86) version 6.2
Java Version: 1.7.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 107891152 bytes (102 MB) / 287322112 bytes (274 MB) up to 1037959168 bytes (989 MB)
JVM Flags: 2 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
FML: MCP v9.01-pre FML v7.2.156.1061 Minecraft Forge 10.12.1.1061 Optifine OptiFine_1.7.2_HD_U_C2 4 mods loaded, 4 mods active
mcp{8.09} [Minecraft Coder Pack] (minecraft.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available
FML{7.2.156.1061} [Forge Mod Loader] (forge-1.7.2-10.12.1.1061.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available
Forge{10.12.1.1061} [Minecraft Forge] (forge-1.7.2-10.12.1.1061.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available
BiomesOPlenty{2.0.0} [Biomes O' Plenty] (BiomesOPlenty-1.7.2-2.0.0.762-universal.jar) Unloaded->Constructed->Pre-initialized->Initialized->Post-initialized->Available->Available
Profiler Position: N/A (disabled)
Vec3 Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
Player Count: 0 / 8; []
Type: Integrated Server (map_client.txt)
Is Modded: Definitely; Client brand changed to 'fml,forge'