So one of the people on my mod's dev team told me that the server crashes by java.lang.NoClassDefFoundError: net/minecraft/client/entity/EntityPlayerSP and I have no idea what is causing that crash and how to fix it. It doesn't crash on my computer.

1 hour ago, Spaceboy Ross said:

EntityPlayerSP

EntityPlayerSinglePlayer...

1 hour ago, Spaceboy Ross said:

client

 

1 hour ago, Spaceboy Ross said:

NoClassDefFoundError

Hmm... I wonder

https://mcforge.readthedocs.io/en/latest/concepts/sides/

you trying to access client side only classes which don’t exist on the server from the server

My mod has never had this issue before, it just all of a sudden appeared. I've attached the log ive received.

Spoiler

---- Minecraft Crash Report ----
// Don't do that.

Time: 18-10-11 下午9:59
Description: Exception in server tick loop

net.minecraftforge.fml.common.LoaderException: java.lang.NoClassDefFoundError: net/minecraft/client/entity/EntityPlayerSP
    at net.minecraftforge.fml.common.AutomaticEventSubscriber.inject(AutomaticEventSubscriber.java:89)
    at net.minecraftforge.fml.common.FMLModContainer.constructMod(FMLModContainer.java:604)
    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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
    at com.google.common.eventbus.EventBus.post(EventBus.java:217)
    at net.minecraftforge.fml.common.LoadController.sendEventToModContainer(LoadController.java:218)
    at net.minecraftforge.fml.common.LoadController.propogateStateMessage(LoadController.java:196)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at com.google.common.eventbus.Subscriber.invokeSubscriberMethod(Subscriber.java:91)
    at com.google.common.eventbus.Subscriber$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$PerThreadQueuedDispatcher.dispatch(Dispatcher.java:116)
    at com.google.common.eventbus.EventBus.post(EventBus.java:217)
    at net.minecraftforge.fml.common.LoadController.distributeStateMessage(LoadController.java:135)
    at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:593)
    at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:97)
    at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:332)
    at net.minecraft.server.dedicated.DedicatedServer.init(DedicatedServer.java:128)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:552)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: net/minecraft/client/entity/EntityPlayerSP
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Unknown Source)
    at java.lang.Class.privateGetPublicMethods(Unknown Source)
    at java.lang.Class.getMethods(Unknown Source)
    at net.minecraftforge.fml.common.eventhandler.EventBus.register(EventBus.java:82)
    at net.minecraftforge.fml.common.AutomaticEventSubscriber.inject(AutomaticEventSubscriber.java:82)
    ... 32 more
Caused by: java.lang.ClassNotFoundException: net.minecraft.client.entity.EntityPlayerSP
    at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 38 more
Caused by: net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerException: Exception in class transformer net.minecraftforge.fml.common.asm.transformers.SideTransformer@7e75bf2d from coremod FMLCorePlugin
    at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:262)
    at net.minecraft.launchwrapper.LaunchClassLoader.runTransformers(LaunchClassLoader.java:279)
    at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:176)
    ... 40 more
Caused by: java.lang.RuntimeException: Attempted to load class net/minecraft/client/entity/EntityPlayerSP for invalid side SERVER
    at net.minecraftforge.fml.common.asm.transformers.SideTransformer.transform(SideTransformer.java:62)
    at net.minecraftforge.fml.common.asm.ASMTransformerWrapper$TransformerWrapper.transform(ASMTransformerWrapper.java:258)
    ... 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: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_161, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 877311216 bytes (836 MB) / 1038876672 bytes (990 MB) up to 1038876672 bytes (990 MB)
    JVM Flags: 3 total; -Xincgc -Xmx1024M -Xms1024M
    IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
    FML: MCP 9.42 Powered by Forge 14.23.4.2705 5 mods loaded, 5 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 |
    |:----- |:--------- |:------------ |:-------------------------------- |:--------- |
    | UC    | minecraft | 1.12.2       | minecraft.jar                    | None      |
    | UC    | mcp       | 9.42         | minecraft.jar                    | None      |
    | UC    | FML       | 8.0.99.99    | forgeSrc-1.12.2-14.23.4.2705.jar | None      |
    | UC    | forge     | 14.23.4.2705 | forgeSrc-1.12.2-14.23.4.2705.jar | None      |
    | UE    | gundam    | 1.0.3        | bin                              | None      |

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

 

 

1 hour ago, Spaceboy Ross said:

net.minecraftforge.fml.common.LoaderException: java.lang.NoClassDefFoundError: net/minecraft/client/entity/EntityPlayerSP

It means you're trying to load a client class on the dedicated server. It likely ran fine playing single player, because the client and server are physically the same (but not logically), but once you move the mod to a dedicated server, this will happen. The link about sides that Cadiboo posted should help explain it more.