Error: java.lang.NoClassDefFoundError: cpw/mods/fml/common/IWorldGenerator

[Clasicks6]

I keep on getting this error upon startup. This error may seem to not be related to the mod but I keep on getting this error message every time BigReactors is present within the mod folder. Here is my log file if y'all are interested:
`
---- Minecraft Crash Report ----

WARNING: coremods are present:
Inventory Tweaks Coremod (InventoryTweaks-1.63.jar)
ForgelinPlugin (Forgelin-1.7.4.jar)
HCASM (HammerCore-1.12.2-2.0.2.2.jar)
IELoadingPlugin (ImmersiveEngineering-core-0.12-84.jar)
Contact their authors BEFORE contacting forge

// Oops.

Time: 8/13/18 2:54 PM
Description: Initializing game

java.lang.NoClassDefFoundError: cpw/mods/fml/common/IWorldGenerator
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at net.minecraftforge.fml.common.FMLModContainer.constructMod(FMLModContainer.java:528)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:218)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:196)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:135)
at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:593)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:225)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:466)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
Caused by: java.lang.ClassNotFoundException: cpw.mods.fml.common.IWorldGenerator
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 38 more
Caused by: java.lang.NullPointerException

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

-- Head --
Thread: Client thread
Stacktrace:
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:348)
at net.minecraftforge.fml.common.FMLModContainer.constructMod(FMLModContainer.java:528)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:218)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:196)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$SynchronizedSubscriber.invokeSubscriberMethod(Subscriber.java:150)
at com.google.common.eventbus.Subscriber$1.run(Subscriber.java:76)
at com.google.common.util.concurrent.MoreExecutors$DirectExecutor.execute(MoreExecutors.java:399)
at com.google.common.eventbus.Subscriber.dispatchEvent(Subscriber.java:71)
at com.google.common.eventbus.Dispatcher$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:135)
at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:593)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:225)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:466)

-- Initialization --
Details:
Stacktrace:
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:377)
at net.minecraft.client.main.Main.main(SourceFile:123)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)

-- System Details --
Details:
Minecraft Version: 1.12.2
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_51, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 270177944 bytes (257 MB) / 603979776 bytes (576 MB) up to 6442450944 bytes (6144 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx6G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.4.2707 65 mods loaded, 65 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored

| State | ID                        | Version                  | Source                                              | Signature                                |
|:----- |:------------------------- |:------------------------ |:--------------------------------------------------- |:---------------------------------------- |
| UC    | minecraft                 | 1.12.2                   | minecraft.jar                                       | None                                     |
| UC    | mcp                       | 9.42                     | minecraft.jar                                       | None                                     |
| UC    | FML                       | 8.0.99.99                | forge-1.12.2-14.23.4.2707.jar                       | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UC    | forge                     | 14.23.4.2707             | forge-1.12.2-14.23.4.2707.jar                       | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UC    | appliedenergistics2       | rv5-stable-11            | appliedenergistics2-rv5-stable-11.jar               | None                                     |
| UC    | bibliocraft               | 2.4.5                    | BiblioCraft[v2.4.5][MC1.12.2].jar                   | None                                     |
| UC    | buildcraftlib             | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftcore            | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftbuilders        | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftenergy          | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftfactory         | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftrobotics        | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcraftsilicon         | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | buildcrafttransport       | 7.99.14                  | BuildCraft-Mod-1.12.2.jar                           | None                                     |
| UC    | carpentersblocks          | 3.4.004 POC              | Carpenter's Blocks v3.4.004 POC - MC 1.12.2.jar     | None                                     |
| UC    | codechickenlib            | 3.2.0.345                | CodeChickenLib-1.12.2-3.2.0.345-universal.jar       | f1850c39b2516232a2108a7bd84d1cb5df93b261 |
| UC    | chickenchunks             | 2.4.1.71                 | ChickenChunks-1.12.2-2.4.1.71-universal.jar         | f1850c39b2516232a2108a7bd84d1cb5df93b261 |
| UC    | redstoneflux              | 2.0.2                    | RedstoneFlux-1.12-2.0.2.3-universal.jar             | 8a6abf2cb9e141b866580d369ba6548732eff25f |
| UC    | cofhcore                  | 4.5.2                    | CoFHCore-1.12.2-4.5.2.19-universal.jar              | None                                     |
| UC    | cofhworld                 | 1.2.0                    | CoFHWorld-1.12.2-1.2.0.5-universal.jar              | 8a6abf2cb9e141b866580d369ba6548732eff25f |
| UC    | craftingtweaks            | 8.1.9                    | CraftingTweaks_1.12.2-8.1.9.jar                     | None                                     |
| UC    | extrautils2               | 1.0                      | extrautils2-1.12-1.7.6.jar                          | None                                     |
| UC    | zerocore                  | 1.12-0.1.2.2             | zerocore-1.12-0.1.2.2.jar                           | None                                     |
| U     | bigreactors               | 1.12.2-0.4.5.49          | ExtremeReactors-1.12.2-0.4.5.49.jar                 | None                                     |
| U     | forgelin                  | 1.7.4                    | Forgelin-1.7.4.jar                                  | None                                     |
| U     | forgemultipartcbe         | 2.4.2.60                 | ForgeMultipart-1.12.2-2.4.2.60-universal.jar        | None                                     |
| U     | microblockcbe             | 2.4.2.60                 | ForgeMultipart-1.12.2-2.4.2.60-universal.jar        | None                                     |
| U     | minecraftmultipartcbe     | 2.4.2.60                 | ForgeMultipart-1.12.2-2.4.2.60-universal.jar        | None                                     |
| U     | hammercore                | 2.0.2.2                  | HammerCore-1.12.2-2.0.2.2.jar                       | None                                     |
| U     | icbmclassic               | 1.12.2-3.0.0.29          | ICBM-classic-1.12.2-3.0.0b29.jar                    | None                                     |
| U     | ichunutil                 | 7.1.4                    | iChunUtil-1.12.2-7.1.4.jar                          | None                                     |
| U     | teslacorelib              | 1.0.14                   | tesla-core-lib-1.12.2-1.0.14.jar                    | None                                     |
| U     | industrialforegoing       | 1.12.2-1.12.1            | Industrial-Foregoing-Mod-1.12.2.jar                 | None                                     |
| U     | ic2                       | 2.8.73-ex112             | industrialcraft-2-2.8.73-ex112.jar                  | None                                     |
| U     | inventorytweaks           | 1.63+release.109.220f184 | InventoryTweaks-1.63.jar                            | None                                     |
| U     | ironchest                 | 1.12.2-7.0.40.824        | ironchest-1.12.2-7.0.40.824.jar                     | None                                     |
| U     | jei                       | 4.11.0.202               | jei_1.12.2-4.11.0.202.jar                           | None                                     |
| U     | mantle                    | 1.12-1.3.2.24            | Mantle-1.12-1.3.2.24.jar                            | None                                     |
| U     | mcjtylib_ng               | 3.0.2                    | mcjtylib-1.12-3.0.2.jar                             | None                                     |
| U     | mrtjpcore                 | 2.1.3.35                 | MrTJPCore-1.12.2-2.1.3.35-universal.jar             | None                                     |
| U     | nei                       | 2.4.1                    | NotEnoughItems-1.12.2-2.4.1.238-universal.jar       | None                                     |
| U     | notenoughwands            | 1.7.0                    | notenoughwands-1.12-1.7.0.jar                       | None                                     |
| U     | projectred-core           | 4.9.0.86                 | ProjectRed-Base-1.12.2.jar                          | None                                     |
| U     | projectred-compat         | 1.0                      | ProjectRed-Compat-1.12.2.jar                        | None                                     |
| U     | projectred-integration    | 4.9.0.86                 | ProjectRed-Integration-1.12.2.jar                   | None                                     |
| U     | projectred-transmission   | 4.9.0.86                 | ProjectRed-Integration-1.12.2.jar                   | None                                     |
| U     | projectred-fabrication    | 4.9.0.86                 | ProjectRed-Fabrication-1.12.2.jar                   | None                                     |
| U     | projectred-illumination   | 4.9.0.86                 | ProjectRed-Lighting-1.12.2.jar                      | None                                     |
| U     | projectred-expansion      | 1.0                      | ProjectRed-Mechanical-1.12.2.jar                    | None                                     |
| U     | projectred-relocation     | 1.0                      | ProjectRed-Mechanical-1.12.2.jar                    | None                                     |
| U     | projectred-transportation | 1.0                      | ProjectRed-Mechanical-1.12.2.jar                    | None                                     |
| U     | projectred-exploration    | 4.9.0.86                 | ProjectRed-World-1.12.2.jar                         | None                                     |
| U     | thermalfoundation         | 2.5.0                    | ThermalFoundation-1.12.2-2.5.0.19-universal.jar     | None                                     |
| U     | thermalexpansion          | 5.5.0                    | ThermalExpansion-1.12.2-5.5.0.29-universal.jar      | None                                     |
| U     | thermalcultivation        | 0.3.0                    | ThermalCultivation-1.12.2-0.3.0.7-universal (1).jar | None                                     |
| U     | thermaldynamics           | 2.5.1                    | ThermalDynamics-1.12.2-2.5.1.14-universal.jar       | None                                     |
| U     | thermalinnovation         | 0.3.0                    | ThermalInnovation-1.12.2-0.3.0.7-universal (1).jar  | None                                     |
| U     | bspkrscore                | at_0.9                   | TreeCapitator-Mod-1.12.jar                          | None                                     |
| U     | treecapitator             | at_0.9                   | TreeCapitator-Mod-1.12.jar                          | None                                     |
| U     | uteamcore                 | 1.1.2-60                 | u_team_core-1.12.2-v1.1.2-60.jar                    | None                                     |
| U     | usefulbackpacks           | 1.1.1.6                  | useful_backpacks-1.12.2-v1.1.1.6.jar                | None                                     |
| U     | wrcbe                     | 2.3.0                    | WR-CBE-1.12.2-2.3.0.27-universal.jar                | None                                     |
| U     | xaerominimap              | 1.15.2                   | Xaeros_Minimap_1.15.2_Forge_1.12.jar                | None                                     |
| U     | immersiveengineering      | 0.12-84                  | ImmersiveEngineering-0.12-84.jar                    | None                                     |
| U     | teslacorelib_registries   | 1.0.14                   | tesla-core-lib-1.12.2-1.0.14.jar                    | None                                     |

Loaded coremods (and transformers): 

Inventory Tweaks Coremod (InventoryTweaks-1.63.jar)
invtweaks.forge.asm.ContainerTransformer
ForgelinPlugin (Forgelin-1.7.4.jar)

HCASM (HammerCore-1.12.2-2.0.2.2.jar)
com.zeitheron.hammercore.asm.HammerCoreTransformer
IELoadingPlugin (ImmersiveEngineering-core-0.12-84.jar)
blusunrize.immersiveengineering.common.asm.IEClassTransformer
AE2 Version: stable rv5-stable-11 for Forge 14.23.1.2554
Launched Version: 1.12.2-forge1.12.2-14.23.4.2707
LWJGL: 2.9.4
OpenGL: GeForce GTX 1060 6GB/PCIe/SSE2 GL version 4.6.0 NVIDIA 388.43, NVIDIA Corporation
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: Yes
Is Modded: Definitely; Client brand changed to 'fml,forge'
Type: Client (map_client.txt)
Resource Packs: 
Current Language: English (US)
Profiler Position: N/A (disabled)
CPU: 4x AMD Ryzen 3 1300X Quad-Core Processor `