Server crashes (Can anyone help?)

Can anyone help my server keeps crashing after a hour or so.

---- Minecraft Crash Report ----

WARNING: coremods are present:
SpongeCoremod (spongeforge-1.8.9-1722-3.1.0-BETA-1136.jar)
Contact their authors BEFORE contacting forge

// I bet Cylons wouldn’t have this problem.

Time: 2/12/17 9:34 AM
Description: Exception in server tick loop

java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.lang.String
at org.spongepowered.mod.plugin.SpongeModPluginContainer.getSortingRules(
at net.minecraftforge.fml.common.Loader.sortModList(
at net.minecraftforge.fml.common.Loader.loadMods(
at net.minecraftforge.fml.server.FMLServerHandler.beginServerLoading(
at net.minecraftforge.fml.common.FMLCommonHandler.onServerStart(
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(
at Source)

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

– System Details –
Minecraft Version: 1.8.9
Operating System: Linux (amd64) version 2.6.32-573.22.1.el6.x86_64
Java Version: 1.8.0_40, Oracle Corporation
Java VM Version: Java HotSpot™ 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 235135128 bytes (224 MB) / 1275592704 bytes (1216 MB) up to 2863661056 bytes (2731 MB)
JVM Flags: 3 total; -Xmx3072M -Xms256M -XX:MaxPermSize=256m
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP 9.19 Powered by Forge 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
U mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
U FML{} [Forge Mod Loader] (custom.jar)
U Forge{} [Minecraft Forge] (custom.jar)
U sponge{1.8.9-1722-3.1.0-BETA-1136} [SpongeForge] (spongeforge-1.8.9-1722-3.1.0-BETA-1136.jar)
U io.github.hsyyid.essentialcmds{@project.informativeVersion@} [EssentialCmds] (EssentialCmds-1.8.9-8.1.14-universal.jar)
U pixelmon{4.3.1} [Pixelmon] (Pixelmon-1.8.9-4.3.1-universal.jar)
U RTG{1.8.9} [Realistic Terrain Generation] (RTG-1.8.9-
Loaded coremods (and transformers):
SpongeCoremod (spongeforge-1.8.9-1722-3.1.0-BETA-1136.jar)
Profiler Position: N/A (disabled)
Is Modded: Definitely; Server brand changed to ‘fml,forge,SpongeForge’
Type: Dedicated Server (map_server.txt)

SpongeForge for 1.8.9 is no longer supported, and has many bugs which have been fixed in newer versions of Sponge. I strongly reccomend updating to 1.10 or 1.11

Moving from Pixelmon 4.3.1 to 5.0.1 will be really easy, and you will see performance improvements. We have currently dropped our 1.8.9 branch, so I strongly suggest moving to 1.10.2. If you need Pixelmon support, you can contact us on our Discord, here.