Hi.

 

I know this error is already in the FAQ's, but all it says is to install Optifine after Forge, which I did. 

 

Here's the crash log:

 

---- Minecraft Crash Report ----
// Sorry

Time: 02/04/20 10:35
Description: Unexpected error

java.lang.NoSuchMethodError: net.minecraft.client.renderer.entity.EntityRendererManager.validateRendererExistence()V
    at net.minecraftforge.fml.client.registry.RenderingRegistry.loadEntityRenderers(RenderingRegistry.java:50) ~[?:?] {re:classloading}
    at net.minecraftforge.fml.client.ClientModLoader.postSidedRunnable(ClientModLoader.java:127) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraftforge.fml.ModLoader.lambda$loadMods$14(ModLoader.java:158) ~[?:?] {re:classloading}
    at net.minecraft.resources.AsyncReloader.func_219557_a(SourceFile:71) ~[?:?] {re:classloading}
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(ThreadTaskExecutor.java:173) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
    at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) ~[?:?] {re:classloading}
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(ThreadTaskExecutor.java:135) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
    at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(ThreadTaskExecutor.java:115) ~[?:?] {re:classloading,pl:accesstransformer:B,xf:OptiFine:default}
    at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:898) ~[?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
    at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:554) ~[?:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
    at net.minecraft.client.main.Main.main(SourceFile:204) ~[1.15.2-forge-31.1.0.jar:?] {re:classloading}
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_74] {}
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_74] {}
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_74] {}
    at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_74] {}
    at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:56) ~[forge-1.15.2-31.1.0.jar:31.1] {}
    at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-5.0.0-milestone.4.jar:?] {}
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-5.0.0-milestone.4.jar:?] {}
    at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-5.0.0-milestone.4.jar:?] {}
    at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-5.0.0-milestone.4.jar:?] {}
    at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-5.0.0-milestone.4.jar:?] {}

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

-- System Details --
Details:
    Minecraft Version: 1.15.2
    Minecraft Version ID: 1.15.2
    Operating System: Mac OS X (x86_64) version 10.11.6
    Java Version: 1.8.0_74, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 1230204312 bytes (1173 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB)
    CPUs: 8
    JVM Flags: 8 total; -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    ModLauncher: 5.0.0-milestone.4+67+b1a340b
    ModLauncher launch target: fmlclient
    ModLauncher naming: srg
    ModLauncher services: 
        /eventbus-2.0.0-milestone.1-service.jar eventbus PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar object_holder_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar runtime_enum_extender PLUGINSERVICE 
        /accesstransformers-2.0.0-milestone.1-shadowed.jar accesstransformer PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar capability_inject_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.0.jar runtimedistcleaner PLUGINSERVICE 
        /preview_OptiFine_1.15.2_HD_U_G1_pre1.jar OptiFine TRANSFORMATIONSERVICE 
        /forge-1.15.2-31.1.0.jar fml TRANSFORMATIONSERVICE 
    FML: 31.1
    Forge: net.minecraftforge:31.1.0
    FML Language Providers: 
        [email protected]
        minecraft@1
    Mod List: 
        forge-1.15.2-31.1.0-client.jar Minecraft {[email protected] ENQUEUE_IMC}
        forge-1.15.2-31.1.0-universal.jar Forge {[email protected] ENQUEUE_IMC}
        worldedit-forge-mc1.15.2-7.1.0.jar WorldEdit {[email protected];48cc31c ENQUEUE_IMC}
        TerraForged-1.15.2-0.0.10.jar TerraForged {[email protected] ENQUEUE_IMC}
    Launched Version: 1.15.2-forge-31.1.0
    Backend library: LWJGL version 3.2.1 build 12
    Backend API: Intel HD Graphics 4000 OpenGL Engine GL version 2.1 INTEL-10.14.74, Intel Inc.
    GL Caps: Using framebuffer using ARB_framebuffer_object extension
    Using VBOs: Yes
    Is Modded: Definitely; Client brand changed to 'forge'
    Type: Client (map_client.txt)
    Resource Packs: 
    Current Language: ~~ERROR~~ NullPointerException: null
    CPU: 8x Intel(R) Core(TM) i7-3615QM CPU @ 2.30GHz
    OptiFine Version: OptiFine_1.15.2_HD_U_G1_pre1
    OptiFine Build: 20200213-173014
    Render Distance Chunks: 8
    Mipmaps: 4
    Anisotropic Filtering: 1
    Antialiasing: 0
    Multitexture: false
    Shaders: null
    OpenGlVersion: 2.1 INTEL-10.14.74
    OpenGlRenderer: Intel HD Graphics 4000 OpenGL Engine
    OpenGlVendor: Intel Inc.
    CpuCount: 8

 

I think it's just because I'm using OS X, but any advice appreciated.  

Optifine creates a new installation in my launcher which works, but I can't run it in my Forge installation with my other Forge mods, doing so gives me the above crash.

 

I Installed Forge first, then moved Optifine to mods folder, then double clicked it to run the installer. Is this not the right process?

I give up.

If you check the changelog for Optifine 1.15.2, it says that it's not compatible with Forge.