I think this is IC2NuclearControl, since it logs with FATAL level about an energy system, then there is a huge message bout mekanism class missing - and it is:
[20:21:57] [Client thread/FATAL] [IC2NuclearControl]: Another Energy System is Loaded. Adding Intergration!
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: java.lang.ClassNotFoundException: mekanism.api.energy.IStrictEnergyStorage
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.Class.forName0(Native Method)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.Class.forName(Class.java:348)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at shedar.mods.ic2.nuclearcontrol.crossmod.mekanism.CrossMekanism.<init>(CrossMekanism.java:16)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at shedar.mods.ic2.nuclearcontrol.crossmod.CrossModLoader.postinit(CrossModLoader.java:30)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at shedar.mods.ic2.nuclearcontrol.IC2NuclearControl.postInit(IC2NuclearControl.java:207)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.reflect.Method.invoke(Method.java:498)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:532)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.reflect.Method.invoke(Method.java:498)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.post(EventBus.java:275)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:212)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:190)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.reflect.Method.invoke(Method.java:498)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at com.google.common.eventbus.EventBus.post(EventBus.java:275)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:119)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.common.Loader.initializeMods(Loader.java:742)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at cpw.mods.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:311)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:552)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:878)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.client.main.Main.main(SourceFile:148)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.reflect.Method.invoke(Method.java:498)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at java.lang.reflect.Method.invoke(Method.java:498)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:236)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:297)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at org.multimc.EntryPoint.listen(EntryPoint.java:162)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: at org.multimc.EntryPoint.main(EntryPoint.java:53)
[20:21:57] [Client thread/INFO] [STDERR]: [java.lang.Throwable$WrappedPrintStream:println:748]: Caused by: java.lang.NullPointerException
I think this is IC2NuclearControl, since it logs with FATAL level about an energy system, then there is a huge message bout mekanism class missing - and it is: