The following stack trace was produced upon attempting to start a custom modpack from MultiMC:

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Mod Tweaker (modtweaker)
Caused by: java.lang.IllegalAccessError: tried to access field de.ellpeck.actuallyadditions.api.recipe.EmpowererRecipe.output from class com.blamejared.compat.actuallyaddition.Empowerer$Add
at com.blamejared.compat.actuallyaddition.Empowerer$Add.getRecipeInfo(Empowerer.java:46)
at com.blamejared.compat.actuallyaddition.Empowerer$Add.getRecipeInfo(Empowerer.java:38)
at com.blamejared.mtlib.utils.BaseListModification.getRecipeInfo(BaseListModification.java:24)
at com.blamejared.mtlib.utils.BaseListAddition.describe(BaseListAddition.java:42)
at crafttweaker.runtime.CrTTweaker.apply(CrTTweaker.java:47)
at crafttweaker.CraftTweakerAPI.apply(CraftTweakerAPI.java:135)
at java.lang.Iterable.forEach(Unknown Source)
at com.blamejared.ModTweaker.loadComplete(ModTweaker.java:43)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:627)
at sun.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:218)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:196)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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.initializeMods(Loader.java:752)
at net.minecraftforge.fml.client.FMLClientHandler.finishMinecraftLoading(FMLClientHandler.java:329)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:534)
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(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196)
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231)
at org.multimc.EntryPoint.listen(EntryPoint.java:143)
at org.multimc.EntryPoint.main(EntryPoint.java:34)

This Error call appears to have resulted from a class version change during runtime, making the output field of an Empowerer recipe inaccessible.

Relevant version numbers:

• Forge: 14.23.4.2705
• Actually Additions: 1.12.2-r137
• ModTweaker: 4.0.12

Not an AA issue