Minecraft Mod added to my Forge Server but crashes

---- Minecraft Crash Report ----

WARNING: coremods are present:
SpongeCoremod (spongeforge-1.12.2-2825-7.1.6 (1).jar)
Contact their authors BEFORE contacting forge

// Oh - I know what I did wrong!

Description: Exception in server tick loop

java.lang.NoClassDefFoundError: twilightforest/block/BlockTFFluid
at twilightforest.block.RegisterBlockEvent.registerFluidBlock(RegisterBlockEvent.java:246)
at twilightforest.block.RegisterBlockEvent.registerFluidBlock(RegisterBlockEvent.java:242)
at twilightforest.block.RegisterBlockEvent.onRegisterBlocks(RegisterBlockEvent.java:140)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_7_RegisterBlockEvent_onRegisterBlocks_Register.invoke(.dynamic)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
at net.minecraftforge.fml.common.eventhandler.EventBus$1.invoke(EventBus.java:144)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:759)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:706)
at net.minecraftforge.registries.GameData.fireRegistryEvents(GameData.java:775)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:628)
at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:99)
at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:333)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:125)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: twilightforest.block.BlockTFFluid
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:191)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
… 15 more
Caused by: java.lang.NoClassDefFoundError: net/minecraftforge/fluids/BlockFluidClassic
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknown Source)
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:182)
… 17 more
Caused by: java.lang.ClassNotFoundException: net.minecraftforge.fluids.BlockFluidClassic
at net.minecraft.launchwrapper.LaunchClassLoader.findClass(LaunchClassLoader.java:101)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
… 21 more

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

– Head –
Thread: Server thread
Stacktrace:
at twilightforest.block.RegisterBlockEvent.registerFluidBlock(RegisterBlockEvent.java:246)
at twilightforest.block.RegisterBlockEvent.registerFluidBlock(RegisterBlockEvent.java:242)
at twilightforest.block.RegisterBlockEvent.onRegisterBlocks(RegisterBlockEvent.java:140)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_7_RegisterBlockEvent_onRegisterBlocks_Register.invoke(.dynamic)
at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
at net.minecraftforge.fml.common.eventhandler.EventBus$1.invoke(EventBus.java:144)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:759)
at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:706)
at net.minecraftforge.registries.GameData.fireRegistryEvents(GameData.java:775)
at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:628)

– Sponge PhaseTracker –
Details:
Phase Stack: [Empty stack]
Stacktrace:
at net.minecraft.server.MinecraftServer.handler$onCrashReport$zjo000(MinecraftServer.java:3980)
at net.minecraft.server.MinecraftServer.func_71230_b(MinecraftServer.java:889)
at net.minecraft.server.dedicated.DedicatedServer.func_71230_b(DedicatedServer.java:371)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:558)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 1.12.2
Java Version: 1.8.0_211, Oracle Corporation
Java VM Version: Java HotSpot™ 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 2772233864 bytes (2643 MB) / 3079667712 bytes (2937 MB) up to 3079667712 bytes (2937 MB)
JVM Flags: 2 total; -Xms3G -Xmx3G
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.5.2768 8 mods loaded, 8 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                                |
|:----- |:-------------- |:----------------- |:------------------------------------------- |:---------------------------------------- |
| UCH   | minecraft      | 1.12.2            | minecraft.jar                               | None                                     |
| UCH   | mcp            | 9.42              | minecraft.jar                               | None                                     |
| UCH   | FML            | 8.0.99.99         | server.jar                                  | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCH   | forge          | 14.23.5.2768      | server.jar                                  | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCH   | spongeapi      | 7.1.0-fb496dbf0   | spongeforge-1.12.2-2825-7.1.6 (1).jar       | None                                     |
| UCH   | sponge         | 1.12.2-7.1.6      | spongeforge-1.12.2-2825-7.1.6 (1).jar       | None                                     |
| UCH   | spongeforge    | 1.12.2-2825-7.1.6 | spongeforge-1.12.2-2825-7.1.6 (1).jar       | None                                     |
| UCH   | twilightforest | 3.9.888           | twilightforest-1.12.2-3.9.888-universal.jar | None                                     |

Loaded coremods (and transformers): 

SpongeCoremod (spongeforge-1.12.2-2825-7.1.6 (1).jar)
org.spongepowered.common.launch.transformer.SpongeSuperclassTransformer
Profiler Position: N/A (disabled)
Is Modded: Definitely; Server brand changed to ‘fml,forge,sponge’
Type: Dedicated Server (map_server.txt)

Does anyone know why this crashes? I tried putting twilight mod but it crashes my server

For one, it looks like you might not have enough ram allocated to the server to run everything. that is a fairly common cause for NoClassDef errors of forge and minecraft classes.

Second, is this issue occurring if Sponge is not installed? If it is still occurring when Sponge is removed, it is likely an issue that should be reported/discussed with the TF mod developer(s).

I would recommend trying to increase the amount of ram first though, and seeing if that makes a difference.

–edit: also make sure that the version of forge you have matches that of the twilight forest mod.