I have already removed the MOD from the MODs folder in reinstalled the server software.
---- Minecraft Crash Report ----
// Ouch. That hurt 
Time: 4/29/20 10:05 PM
Description: Exception in server tick loop
Duplicate Mods:
voxelmap : /aternos/server/./mods/forgemod_VoxelMap-1.9.16_for_1.12.2.jar
voxelmap : /aternos/server/./mods/forgemod_VoxelMap-1.9.16_for_1.12.2.jar
net.minecraftforge.fml.common.DuplicateModsFoundException
at net.minecraftforge.fml.common.Loader.identifyDuplicates(Loader.java:466)
at net.minecraftforge.fml.common.Loader.identifyMods(Loader.java:428)
at net.minecraftforge.fml.common.Loader.loadMods(Loader.java:568)
at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:98)
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(Thread.java:748)
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 4.15.0-91-generic
Java Version: 1.8.0_242, Oracle Corporation
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 570619920 bytes (544 MB) / 1009778688 bytes (963 MB) up to 1398276096 bytes (1333 MB)
JVM Flags: 3 total; -XX:MaxMetaspaceSize=200M -Xmx1500M -Xms750M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.42 Powered by Forge 14.23.5.2847 8 mods loaded, 0 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 |
|:----- |:---------------- |:------------ |:--------------------------------------- |:--------- |
| | minecraft | 1.12.2 | minecraft.jar | None |
| | mcp | 9.42 | minecraft.jar | None |
| | FML | 8.0.99.99 | forge.jar | None |
| | forge | 14.23.5.2847 | forge.jar | None |
| | voxelmap | 1.9.16 | forgemod_VoxelMap-1.9.16_for_1.12.2.jar | None |
| | cavern | 1.10.6 | Cavern_1.12.2-v1.10.6.jar | None |
| | voxelmap | 1.9.16 | forgemod_VoxelMap-1.9.16_for_1.12.2.jar | None |
| | keepinginventory | 2.4 | KeepingInventory-1.12.2-2.4.jar | 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)