Version Info

• Minecraft: 1.12.2
• Simple Magnets: simplemagnets-1.1.10-forge-mc1.12

Steps to Reproduce
Run a server with Simple Magnets and all dependencies needed for Simple Magnets

Crash report (~/logs/latest.log)
---- Minecraft Crash Report ----

WARNING: coremods are present:
SuperMartijn642's Core Lib Plugin (_supermartijn642corelib-1.1.17-forge-mc1.12.jar)
Contact their authors BEFORE contacting forge

// Don't be sad, have a hug! <3

Time: 3/24/24 4:00 PM
Description: Exception in server tick loop

net.minecraftforge.fml.common.LoaderExceptionModCrash: Caught exception from Simple Magnets (simplemagnets)
Caused by: java.lang.NoClassDefFoundError: net/minecraft/client/settings/KeyBinding
at com.supermartijn642.simplemagnets.SimpleMagnetsClient.registerKeyBindings(SimpleMagnetsClient.java:37)
at com.supermartijn642.simplemagnets.SimpleMagnets.init(SimpleMagnets.java:95)
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:498)
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:498)
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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:219)
at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:197)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
at com.google.common.eventbus.Subscriber$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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
at com.google.common.eventbus.EventBus.post(EventBus.java:217)
at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:136)
at net.minecraftforge.fml.common.Loader.initializeMods(Loader.java:749)
at net.minecraftforge.fml.server.FMLServerHandler.finishServerLoading(FMLServerHandler.java:108)
at net.minecraftforge.fml.common.FMLCommonHandler.onServerStarted(FMLCommonHandler.java:338)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:219)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.settings.KeyBinding
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
... 38 more
Caused by: net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerException: Exception in class transformer net.minecraftforge.fml.common.asm.transformers.SideTransformer@4564e94b from coremod FMLCorePlugin
at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:260)
at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176)
... 40 more
Caused by: java.lang.RuntimeException: Attempted to load class bhy for invalid side SERVER
at net.minecraftforge.fml.common.asm.transformers.SideTransformer.transform(SideTransformer.java:62)
at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:256)
... 42 more

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: Linux (amd64) version 5.15.146.1-microsoft-standard-WSL2
Java Version: 1.8.0_312, Temurin
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Temurin
Memory: 3317956192 bytes (3164 MB) / 4116185088 bytes (3925 MB) up to 7635730432 bytes (7282 MB)
JVM Flags: 2 total; -Xmx8G -Xms4G
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.5.2859 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                                |
|:----- |:------------------------ |:------------ |:----------------------------------------------- |:---------------------------------------- |
| LCHI  | minecraft                | 1.12.2       | minecraft.jar                                   | None                                     |
| LCHI  | mcp                      | 9.42         | minecraft.jar                                   | None                                     |
| LCHI  | FML                      | 8.0.99.99    | forge-1.12.2-14.23.5.2859.jar                   | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| LCHI  | forge                    | 14.23.5.2859 | forge-1.12.2-14.23.5.2859.jar                   | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| LCHI  | supermartijn642corelib   | 1.1.17       | _supermartijn642corelib-1.1.17-forge-mc1.12.jar | None                                     |
| LCHI  | supermartijn642configlib | 1.1.6        | supermartijn642configlib-1.1.8-forge-mc1.12.jar | None                                     |
| LCHE  | simplemagnets            | 1.1.10       | simplemagnets-1.1.10-forge-mc1.12.jar           | None                                     |

Loaded coremods (and transformers): 

SuperMartijn642's Core Lib Plugin (_supermartijn642corelib-1.1.17-forge-mc1.12.jar)

Profiler Position: N/A (disabled)
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)

Getting this as well. Seems it's trying to call client only code on the server

Yup this issue was filed after a discussion on Discord. The problem is a missing client-side check here:

I have fixed it now in version 1.1.11 of Simple Magnets for Forge 1.12.
Thank you for reporting the issue!