I recently upgraded to the new Farseek update, as well as streams update.
However, after doing so, launching the server would result in this error:

`Time: 6/3/18 4:59 AM
Description: Exception in server tick loop

java.util.ConcurrentModificationException
at java.util.HashMap$HashIterator.nextNode(HashMap.java:1437)
at java.util.HashMap$KeyIterator.next(HashMap.java:1461)
at net.minecraft.entity.EntityTracker.func_72788_a(EntityTracker.java:290)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:779)
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:396)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:745)
`
After a bit of sleuthing I pinned the error to this mod.

Some thing to note.
I have only experienced this error when upgrading to the newest version on a server that has ran the previous version. Starting a new world does not cause the crash to occur.

Hi Jophire, thanks for reporting this. I have a few questions to help investigating this:

• Could you paste your full game log including the list of loaded mods?
• Does this happen only once after updating your world and then goes away after restarting, or does it keep happening and preventing you from playing?
• If you run your world for a few more minutes with the old versions and then upgrade, does it still happen? (I'm asking this in the off chance a specific entity ticking schedule is causing it).

Thanks! (Also anyone reading this, if you experienced the same issue in your own servers please let me know.)

Just updated to Forge 14.23.4.2705 and got the crash on server startup
Full crashlog: https://pastebin.com/waSbFQqx

Was using 14.23.3.266x (don't remember precisely, maybe 2665) and got no crash

Hi Insane-96, I don't think this one is from Farseek - it seems your version of Forge (2668 according to your crashlog) isn't compatible with your version of WearableBackpacks. (This is the line that's crashing). Can you try again with the latest Forge?

Seems like that I've got the error only one time, and I've sent you the wrong crash log. I'll report if happens again.

There it is https://pastebin.com/7YcBq2Jx crashed again

It looks like it can't find the Scala libraries normally included with Forge. Are you using a custom launcher? Do you have a complete log files including your list of mods etc.?

Thanks for the update Insane-96. If this re-occurs could you please open a separate issue? (The original crash reported by @Jophire is different from yours.) Thanks!

Sure sorry, I thought it was the same error.