After doing a lot of mod updates I had some crashing issues and have spent time narrowing it down to a selective set of mods.

AncientTrees-1.7.10-1.6.2.jar
extrautilities-1.2.11.jar
forestry_1.7.10-3.6.4.22.jar
HardcoreEnderExpansion MC-1.7.10 v1.8.3.jar

If all three of those other mods are on then it appears HEE crashes with the following crash report, if I disable any one of those it loads.

Hope you can advise? :)

---- Minecraft Crash Report ----
// This doesn't make any sense!

Time: 09/09/15 16:38
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
at chylex.hee.proxy.NotificationCommonProxy.tryDeliverNotifications(NotificationCommonProxy.java:50)
at chylex.hee.proxy.NotificationCommonProxy.report(NotificationCommonProxy.java:31)
at chylex.hee.system.logging.Log.warn(Log.java:73)
at chylex.hee.mechanics.misc.StardustDecomposition.addFromString(StardustDecomposition.java:122)
at chylex.hee.system.ConfigHandler.loadGeneralConfig(ConfigHandler.java:118)
at chylex.hee.system.ConfigHandler.loadGeneral(ConfigHandler.java:41)
at chylex.hee.proxy.ModCommonProxy.loadConfiguration(ModCommonProxy.java:12)
at chylex.hee.HardcoreEnderExpansion.onPreInit(HardcoreEnderExpansion.java:95)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at cpw.mods.fml.common.FMLModContainer.handleModStateEvent(FMLModContainer.java:532)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
at com.google.common.eventbus.EventBus.post(EventBus.java:275)
at cpw.mods.fml.common.LoadController.sendEventToModContainer(LoadController.java:212)
at cpw.mods.fml.common.LoadController.propogateStateMessage(LoadController.java:190)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at com.google.common.eventbus.EventSubscriber.handleEvent(EventSubscriber.java:74)
at com.google.common.eventbus.SynchronizedEventSubscriber.handleEvent(SynchronizedEventSubscriber.java:47)
at com.google.common.eventbus.EventBus.dispatch(EventBus.java:322)
at com.google.common.eventbus.EventBus.dispatchQueuedEvents(EventBus.java:304)
at com.google.common.eventbus.EventBus.post(EventBus.java:275)
at cpw.mods.fml.common.LoadController.distributeStateMessage(LoadController.java:119)
at cpw.mods.fml.common.Loader.preinitializeMods(Loader.java:556)
at cpw.mods.fml.server.FMLServerHandler.beginServerLoading(FMLServerHandler.java:88)
at cpw.mods.fml.common.FMLCommonHandler.onServerStart(FMLCommonHandler.java:314)
at net.minecraft.server.dedicated.DedicatedServer.func_71197_b(DedicatedServer.java:117)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:387)
at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:685)

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

-- System Details --
Details:
Minecraft Version: 1.7.10
Operating System: Linux (amd64) version 3.19.0-21-generic
Java Version: 1.7.0_79, Oracle Corporation
Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 1404467008 bytes (1339 MB) / 2077753344 bytes (1981 MB) up to 3151495168 bytes (3005 MB)
JVM Flags: 5 total; -Xms2048m -Xmx3072m -XX:PermSize=256m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC
AABB Pool Size: 0 (0 bytes; 0 MB) allocated, 0 (0 bytes; 0 MB) used
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
FML: MCP v9.05 FML v7.10.99.99 Minecraft Forge 10.13.4.1492 16 mods loaded, 16 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCH mcp{9.05} Minecraft Coder Pack
UCH FML{7.10.99.99} Forge Mod Loader
UCH Forge{10.13.4.1492} Minecraft Forge
UCE HardcoreEnderExpansion{1.8.3} [Hardcore Ender Expansion](HardcoreEnderExpansion MC-1.7.10 v1.8.3.jar)
UCH Forestry{3.6.4.22} Forestry for Minecraft
UCH koresample{1.7.10-1.3.2} Kore Sample
UCH dendrology{1.7.10-1.6.2} Ancient Trees
UCH Baubles{1.0.1.10} Baubles
UCH ForgeMultipart{1.2.0.345} Forge Multipart
UCH ExtraUtilities{1.2.11} Extra Utilities
UCH McMultipart{1.2.0.345} Minecraft Multipart Plugin
UCH ForgeRelocation{0.0.1.4} ForgeRelocation
UCH MCFrames{1.0} MCFrames
UCH RelocationFMP{0.0.1.2} RelocationFMP
UCH MrTJPCoreMod{1.1.0.31} MrTJPCore
UCH ForgeMicroblock{1.2.0.345} Forge Microblocks
Profiler Position: N/A (disabled)
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)

Fixed in upcoming update.

Hmm... which of these mods are coremods?

I would suggest not using the stardust decomposition config and using the config API instead, but it won't solve the underlying issue. I would understand if it happened without any other mods (because the code for reporting warnings doesn't seem to be perfectly safe), but right now it looks like some coremod is breaking things or causing HEE to be called too early, so not quite sure.

Actually, this should never happen unless you have debugging enabled. Check your config.

Hah, yes that was it! debugging was on for some reason (Can only assume it was a default of a previous version?). Thanks for responding and helping!

It's never enabled by default, it has a massive performance impact. I'll leave this open because I still need to fix the crash, I never tested debugging in multiplayer.

Odd, as I'm as sure as I can be I didn't enable it, so just assumed it may have been from a previous version that accidentally had it on.. (I've been regularly updating my pack for the best part of a year).

I know there are more mods that can trigger this error than just the 3 i mentioned, I had one of them disabled when I put all my others back and the issue still occurred. This was the error I got before turning off debug: http://pastebin.com/1Fkbj2jg

You should check the logs, it means you have warnings there (in this case it's a config setting that will stop working soon). Debug mode prints all this stuff directly in your chat, so I would definitely not suggest keeping it enabled :P.