If multiple users connecting to a server are using a different Forge version could it cause crashing? Either that or the server mods are my amateur theories. Crash reports appear to be differ but here's one...it crashes often..
---- Minecraft Crash Report ----
// Don't be sad, have a hug! <3
Time: 6/24/15 10:38 PM
Description: Exception in server tick loop
java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1429)
at java.util.HashMap$KeyIterator.next(HashMap.java:1453)
at net.minecraft.entity.EntityTracker.func_72788_a(EntityTracker.java:270)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:716)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:364)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:598)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:478)
at java.lang.Thread.run(Thread.java:745)
A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------
-- System Details --
Details:
Minecraft Version: 1.8
Operating System: Windows 8.1 (amd64) version 6.3
Java Version: 1.8.0_45, Oracle Corporation
Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
Memory: 1997176288 bytes (1904 MB) / 3126853632 bytes (2982 MB) up to 3126853632 bytes (2982 MB)
JVM Flags: 2 total; -Xms3G -Xmx3G
IntCache: cache: 0, tcache: 0, allocated: 13, tallocated: 95
FML: MCP v9.10 FML v8.0.99.99 Minecraft Forge 11.14.3.1450 10 mods loaded, 10 mods active
States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
UCHIJAAAA mcp{9.05} [Minecraft Coder Pack] (minecraft.jar)
UCHIJAAAA FML{8.0.99.99} [Forge Mod Loader] (forge-1.8-11.14.3.1450-universal.jar)
UCHIJAAAA Forge{11.14.3.1450} [Minecraft Forge] (forge-1.8-11.14.3.1450-universal.jar)
UCHIJAAAA k4lib{1.8-1.0.4} [K4Lib] (k4lib-1.8-1.0.4-universal.jar)
UCHIJAAAA colorchat{1.8-1.0.3} [ColorChat] (colorchat-1.8-1.0.3-universal.jar)
UCHIJAAAA landdefender{0.4.0} [Land Defender] (landdefender-0.4.0.jar)
UCHIJAAAA ModControl{1.4} [Mod Control] (ModControl-1.4.jar)
UCHIJAAAA pixelmon{4.0.5} [Pixelmon] (Pixelmon-1.8-4.0.5-universal.jar)
UCHIJAAAA SpawnCommands{2.2.0} [spawnCommands] (SpawnCommands-2.2.0-mc1.8-forge.jar)
UCHIJAAAA worldedit{6.1} [WorldEdit] (worldedit-forge-mc1.8-6.1.jar)
Loaded coremods (and transformers):
Profiler Position: N/A (disabled)
Player Count: 6 / 20; [EntityPlayerMP['Master_Yen'/1148, l='world', x=198.51, y=73.31, z=-161.51], EntityPlayerMP['David8505'/1582, l='world', x=142.06, y=76.02, z=286.19], EntityPlayerMP['iiFazedPvP'/3275, l='world', x=303.23, y=67.02, z=283.55], EntityPlayerMP['ThePizzaDinosaur'/41252, l='world', x=372.61, y=83.00, z=224.40], EntityPlayerMP['Hydra_of_Death'/4722, l='world', x=267.92, y=64.00, z=248.37], EntityPlayerMP['tubs787'/43169, l='world', x=359.50, y=72.00, z=242.07]]
Is Modded: Definitely; Server brand changed to 'fml,forge'
Type: Dedicated Server (map_server.txt)