Can anyone make sense of this error report? Minecraft was just working earlier today and now it decides it wants to give up on life.

 

Spoiler

---- Minecraft Crash Report ----

WARNING: coremods are present:
Contact their authors BEFORE contacting forge

// Don't do that.

Time: 8/3/17 10:46 PM
Description: There was a severe problem during mod loading that has caused the game to fail

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from mercurius_updater (mercurius_updater)
Caused by: java.lang.NoSuchMethodError: net.minecraftforge.fml.relauncher.ReflectionHelper.findMethod(Ljava/lang/Class;Ljava/lang/Object;[Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;
	at net.minecraftforge.mercurius.updater.MercuriusUpdaterMod.invokeEvent(MercuriusUpdaterMod.java:121)
	at net.minecraftforge.mercurius.updater.MercuriusUpdaterMod.preInit(MercuriusUpdaterMod.java:71)
	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:483)
	at net.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:614)
	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:483)
	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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
	at com.google.common.eventbus.EventBus.post(EventBus.java:217)
	at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:252)
	at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:230)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
	at com.google.common.eventbus.Subscriber$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:147)
	at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:604)
	at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:266)
	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:483)
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28)


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

-- System Details --
Details:
	Minecraft Version: 1.12
	Operating System: Windows 10 (amd64) version 10.0
	Java Version: 1.8.0_25, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 118328080 bytes (112 MB) / 295407616 bytes (281 MB) up to 1060372480 bytes (1011 MB)
	JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx1G -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	FML: MCP 9.40 Powered by Forge 14.21.1.2443 Optifine OptiFine_1.12_HD_U_C4 6 mods loaded, 6 mods active
	States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
	UCH	minecraft{1.12} [Minecraft] (minecraft.jar) 
	UCH	mcp{9.19} [Minecraft Coder Pack] (minecraft.jar) 
	UCH	FML{8.0.99.99} [Forge Mod Loader] (forge-1.12-14.21.1.2443.jar) 
	UCH	forge{14.21.1.2443} [Minecraft Forge] (forge-1.12-14.21.1.2443.jar) 
	UCE	mercurius_updater{1.0} [mercurius_updater] (MercuriusUpdater-1.12.jar) 
	UCH	worldedit{6.1.8-SNAPSHOT} [WorldEdit] (worldedit-forge-mc1.12-6.1.8-SNAPSHOT-20170629-dist.jar) 
	Loaded coremods (and transformers): 
	GL info: ' Vendor: 'Intel' Version: '4.0.0 - Build 10.18.10.4358' Renderer: 'Intel(R) HD Graphics 4000'
	OptiFine Version: OptiFine_1.12_HD_U_C4
	Render Distance Chunks: 8
	Mipmaps: 4
	Anisotropic Filtering: 1
	Antialiasing: 0
	Multitexture: false
	Shaders: null
	OpenGlVersion: 4.0.0 - Build 10.18.10.4358
	OpenGlRenderer: Intel(R) HD Graphics 4000
	OpenGlVendor: Intel
	CpuCount: 4

 

 

It seems to be a problem with mercurius. I had the exact same problem, and the way I solved it was deleting the forge profile in the MC launcher, then redownload forge, but disable the option to install mercurius. If you look carefully at the error report, it says there is an error with mercurius.