My Modpack kept crashing and I narrowed it down to this Mod and The Midnight (and llibrary). Where exactly is the Problem with those two Mods?

---- Minecraft Crash Report ----

WARNING: coremods are present:
llibrary (llibrary-core-1.0.11-1.12.2.jar)
midnight (themidnight-0.3.5.jar)
Contact their authors BEFORE contacting forge

// You're mean.

Time: 2/9/21 11:00 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 Midnight (midnight)
Caused by: java.lang.IllegalArgumentException: Failed to register dimension for id -23, One is already registered
at net.minecraftforge.common.DimensionManager.registerDimension(DimensionManager.java:134)
at com.mushroom.midnight.common.registry.ModDimensions.register(ModDimensions.java:12)
at com.mushroom.midnight.Midnight.preInit(Midnight.java:133)
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.minecraftforge.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:637)
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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:219)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:197)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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:136)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:629)
at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:252)
at net.minecraft.client.Minecraft.func_71384_a(Minecraft.java:467)
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:378)
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)

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

-- 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: 653759912 bytes (623 MB) / 1073741824 bytes (1024 MB) up to 7516192768 bytes (7168 MB)
JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx7G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.5.2854 7 mods loaded, 7 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                                |
|:----- |:--------- |:------------ |:----------------------------- |:---------------------------------------- |
| LCH   | minecraft | 1.12.2       | minecraft.jar                 | None                                     |
| LCH   | mcp       | 9.42         | minecraft.jar                 | None                                     |
| LCH   | FML       | 8.0.99.99    | forge-1.12.2-14.23.5.2854.jar | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| LCH   | forge     | 14.23.5.2854 | forge-1.12.2-14.23.5.2854.jar | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| LCH   | llibrary  | 1.7.19       | llibrary-1.7.19-1.12.2.jar    | b9f30a813bee3b9dd5652c460310cfcd54f6b7ec |
| LCH   | fossil    | 8.0.5        | fossilsarcheology-8.0.5.jar   | None                                     |
| LCE   | midnight  | 0.3.5        | themidnight-0.3.5.jar         | None                                     |

Loaded coremods (and transformers): 

llibrary (llibrary-core-1.0.11-1.12.2.jar)
net.ilexiconn.llibrary.server.core.plugin.LLibraryTransformer
net.ilexiconn.llibrary.server.core.patcher.LLibraryRuntimePatcher
midnight (themidnight-0.3.5.jar)
com.mushroom.midnight.core.transformer.MidnightClassTransformer
GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.6.0 NVIDIA 456.71' Renderer: 'GeForce GTX 1060 6GB/PCIe/SSE2'

Failed to register dimension for id -23, One is already registered
Midnight and F&A both try to register dimensions with ID -23 by default, specifically, F&A's Land of Darkness and Midnight's core dimension.
You can change the DimIDs for F&A in the config, so do.