What is wrong with my server! HELP

---- Minecraft Crash Report ----

WARNING: coremods are present:
SpongeCoremod (spongeforge-1.12.2-2705-7.1.0-BETA-3481.jar)
Contact their authors BEFORE contacting forge

// Ooh. Shiny.

Time: 2018-12-06 14:29
Description: Exception in server tick loop

java.lang.RuntimeException: derp
at net.minecraft.world.storage.SaveHandler.redirect$onLoadWorldInfo$bcl000(SaveHandler.java:1073)
at net.minecraft.world.storage.SaveHandler.func_75757_d(SaveHandler.java:122)
at org.spongepowered.common.world.WorldManager.loadAllWorlds(WorldManager.java:711)
at net.minecraft.server.MinecraftServer.func_71247_a(MinecraftServer.java:3545)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:270)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:486)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.RuntimeException: Attempt failed when reading Sponge level data for [world] from file [level_sponge.dat]!
at net.minecraft.world.storage.SaveHandler.loadSpongeDatData(SaveHandler.java:619)
at net.minecraft.world.storage.SaveHandler.redirect$onLoadWorldInfo$bcl000(SaveHandler.java:1071)
… 6 more
Caused by: java.util.zip.ZipException: Not in GZIP format
at java.util.zip.GZIPInputStream.readHeader(Unknown Source)
at java.util.zip.GZIPInputStream.(Unknown Source)
at java.util.zip.GZIPInputStream.(Unknown Source)
at net.minecraft.nbt.CompressedStreamTools.func_74796_a(CompressedStreamTools.java:26)
at net.minecraft.world.storage.SaveHandler.loadSpongeDatData(SaveHandler.java:616)
… 7 more

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

– Head –
Thread: Server thread
Stacktrace:
at net.minecraft.world.storage.SaveHandler.redirect$onLoadWorldInfo$bcl000(SaveHandler.java:1073)
at net.minecraft.world.storage.SaveHandler.func_75757_d(SaveHandler.java:122)

– Sponge PhaseTracker –
Details:
Phase Stack: [Empty stack]
Stacktrace:
at net.minecraft.server.MinecraftServer.handler$onCrashReport$zjk000(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:370)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:558)
at java.lang.Thread.run(Unknown Source)

– System Details –
Details:
Minecraft Version: 1.12.2
Operating System: Windows 10 (amd64) version 10.0
Java Version: 1.8.0_191, Oracle Corporation
Java VM Version: Java HotSpot™ 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 4460371040 bytes (4253 MB) / 6109003776 bytes (5826 MB) up to 6109003776 bytes (5826 MB)
JVM Flags: 2 total; -Xms4G -Xmx6G
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.4.2705 9 mods loaded, 9 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                                |
|:------- |:--------- |:--------------------------- |:------------------------------------------- |:---------------------------------------- |
| UCHIJAA | minecraft | 1.12.2                      | minecraft.jar                               | None                                     |
| UCHIJAA | mcp       | 9.42                        | minecraft.jar                               | None                                     |
| UCHIJAA | FML       | 8.0.99.99                   | forge-1.12.2-14.23.4.2705-universal.jar     | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCHIJAA | forge     | 14.23.4.2705                | forge-1.12.2-14.23.4.2705-universal.jar     | e3c3d50c7c986df74c645c0ac54639741c90a557 |
| UCHIJAA | spongeapi | 7.1.0-ff990df               | spongeforge-1.12.2-2705-7.1.0-BETA-3481.jar | None                                     |
| UCHIJAA | sponge    | 1.12.2-2705-7.1.0-BETA-3481 | spongeforge-1.12.2-2705-7.1.0-BETA-3481.jar | 6729a677746f8cf63ef31881f913ed15d431b7f0 |
| UCHIJAA | luckperms | 4.3.39                      | LuckPerms-Sponge-4.3.39.jar                 | None                                     |
| UCHIJAA | nucleus   | 1.5.5-S7.0                  | Nucleus-1.5.5-S7.0-MC1.12.2-plugin.jar      | None                                     |
| UCHIJAA | pixelmon  | 6.3.4                       | Pixelmon-1.12.2-6.3.4-universal.jar         | None                                     |

Loaded coremods (and transformers): 

SpongeCoremod (spongeforge-1.12.2-2705-7.1.0-BETA-3481.jar)
org.spongepowered.common.launch.transformer.SpongeSuperclassTransformer
Profiler Position: N/A (disabled)
Player Count: 0 / 20; []
Is Modded: Definitely; Server brand changed to ‘fml,forge,sponge’
Type: Dedicated Server (map_server.txt)

This is your issue

Caused by: java.lang.RuntimeException: Attempt 
failed when reading Sponge level data for [world] 
from file [level_sponge.dat]!

Go to your world folder and make a backup. After that delete the level_sponge.dat. from there minecraft should handle the rest