I've been experiencing this exception many times, when my entity dies, or it checks for nearby entities using worldObj.getEntitiesWithinAABB or even when trying to move using moveEntity(motionX, motionY, motionZ),....

2012-08-23 15:53:07 [iNFO] [sTDERR] java.util.ConcurrentModificationException
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at java.util.ArrayList$Itr.next(Unknown Source)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.Chunk.getEntitiesWithinAABBForEntity(Chunk.java:1073)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.World.getEntitiesWithinAABBExcludingEntity(World.java:3337)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.World.getCollidingBoundingBoxes(World.java:1461)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.Entity.moveEntity(Entity.java:657)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at willez.minegicka.Spray.onUpdate(Spray.java:75)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at willez.minegicka.SprayWater.onUpdate(SprayWater.java:41)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.World.updateEntityWithOptionalForce(World.java:2021)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.WorldServer.updateEntityWithOptionalForce(WorldServer.java:538)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.World.updateEntity(World.java:1986)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.World.updateEntities(World.java:1867)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.WorldServer.updateEntities(WorldServer.java:437)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.updateTimeLightAndEntities(MinecraftServer.java:616)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.tick(MinecraftServer.java:547)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.IntegratedServer.tick(IntegratedServer.java:102)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:453)
2012-08-23 15:53:07 [iNFO] [sTDERR] 	at net.minecraft.src.ThreadServerApplication.run(ThreadServerApplication.java:17)

If you're willing zip up your source and send it to me so I can do some testing.

I cant seem to figure out why this is happening as the two threads that deal with the entity list deal with different chunk instances.

So having a mod that can reproduce this and figure out exactly what causes this. If it is indeed Forge, or if its user error.

I zipped my source code here, the package is willez.minegicka

Here's the link. Tell me if you can't download from mf

http://www.mediafire.com/?i5n1cl5o3d21tt6

 

Hope you can solve this

Found the issue, you're spawning entities on the server, using the client thread.

You need to edit your tick handler to use the server ticks.

Aside form that you really need to re-design your mod for the clear separation of client and server, else you're gunna be doomed to be a old outdated single player only mod forever.

alright thanks for the help

well...um....after a few days looking around i don't really know how to fix this errors

Can you show me how exactly i can fix this?

Only access server instances from the server thread and only access client instances from the client thread.

that is so clear thank you