Bukkit

What steps will reproduce the problem?
1. Have 10,000,000 money and "Max-Stack-Size" set to something like 2500
2. Kill yourself and go pickup dropped money all over ground
3. Check console for below errors and notice all your money is gone.

What is the expected output? What do you see instead?
No errors.

What version of the product are you using?
MoneyDrop 2.1.1 on Bukkit 1.5.1-R0.2 (b2754jnks)

Do you have an error log of what happened?
2013-04-15 20:47:37 [SEVERE] Exception in thread "pool-1-thread-8"
2013-04-15 20:47:37 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin MoneyDrop v2.1.1 generated an exception while executing task 199
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at java.util.LinkedList$ListItr.next(Unknown Source)
    at com.iCo6.IO.mini.Mini.read(Mini.java:148)
    at com.iCo6.IO.mini.Mini.update(Mini.java:360)
    at com.iCo6.system.Queried.createAccount(Queried.java:227)
    at com.iCo6.system.Accounts.create(Accounts.java:34)
    at com.iCo6.system.Accounts.create(Accounts.java:29)
    at com.iCo6.system.Accounts.create(Accounts.java:25)
    at com.iCo6.system.Accounts.get(Accounts.java:15)
    at net.milkbowl.vault.economy.plugins.Economy_iConomy6.depositPlayer(Economy_iConomy6.java:156)
    at me.drakespirit.plugins.moneydrop.WalletUpdate.run(WalletUpdate.java:25)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftTask.run(CraftTask.java:53)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more

2013-04-15 20:47:37 [SEVERE] Exception in thread "pool-1-thread-1"
2013-04-15 20:47:37 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin MoneyDrop v2.1.1 generated an exception while executing task 198
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NullPointerException
    at java.util.LinkedList$ListItr.next(Unknown Source)
    at com.iCo6.IO.mini.Mini.read(Mini.java:148)
    at com.iCo6.IO.mini.Mini.update(Mini.java:360)
    at com.iCo6.system.Queried.createAccount(Queried.java:227)
    at com.iCo6.system.Accounts.create(Accounts.java:34)
    at com.iCo6.system.Accounts.create(Accounts.java:29)
    at com.iCo6.system.Accounts.create(Accounts.java:25)
    at com.iCo6.system.Accounts.get(Accounts.java:15)
    at net.milkbowl.vault.economy.plugins.Economy_iConomy6.depositPlayer(Economy_iConomy6.java:156)
    at me.drakespirit.plugins.moneydrop.WalletUpdate.run(WalletUpdate.java:25)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftTask.run(CraftTask.java:53)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more

2013-04-15 20:47:39 [SEVERE] Exception in thread "pool-1-thread-6"
2013-04-15 20:47:39 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin MoneyDrop v2.1.1 generated an exception while executing task 218
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.util.ConcurrentModificationException
    at java.util.LinkedHashMap$LinkedHashIterator.nextEntry(Unknown Source)
    at java.util.LinkedHashMap$KeyIterator.next(Unknown Source)
    at com.iCo6.IO.mini.Mini.update(Mini.java:362)
    at com.iCo6.system.Queried.setBalance(Queried.java:427)
    at com.iCo6.system.Holdings.setBalance(Holdings.java:26)
    at com.iCo6.system.Holdings.math(Holdings.java:103)
    at com.iCo6.system.Holdings.add(Holdings.java:58)
    at net.milkbowl.vault.economy.plugins.Economy_iConomy6.depositPlayer(Economy_iConomy6.java:157)
    at me.drakespirit.plugins.moneydrop.WalletUpdate.run(WalletUpdate.java:25)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftTask.run(CraftTask.java:53)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more

2013-04-15 20:47:46 [SEVERE] Exception in thread "pool-1-thread-19"
2013-04-15 20:47:46 [SEVERE] org.apache.commons.lang.UnhandledException: Plugin MoneyDrop v2.1.1 generated an exception while executing task 244
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.util.ConcurrentModificationException
    at java.util.LinkedList$ListItr.checkForComodification(Unknown Source)
    at java.util.LinkedList$ListItr.next(Unknown Source)
    at com.iCo6.IO.mini.Mini.read(Mini.java:148)
    at com.iCo6.IO.mini.Mini.read(Mini.java:135)
    at com.iCo6.IO.mini.Mini.update(Mini.java:374)
    at com.iCo6.system.Queried.setBalance(Queried.java:427)
    at com.iCo6.system.Holdings.setBalance(Holdings.java:26)
    at com.iCo6.system.Holdings.math(Holdings.java:103)
    at com.iCo6.system.Holdings.add(Holdings.java:58)
    at net.milkbowl.vault.economy.plugins.Economy_iConomy6.depositPlayer(Economy_iConomy6.java:157)
    at me.drakespirit.plugins.moneydrop.WalletUpdate.run(WalletUpdate.java:25)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftTask.run(CraftTask.java:53)
    at org.bukkit.craftbukkit.v1_5_R2.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
    ... 3 more

Please provide any additional information below.
There is no problem if you set Max-Stack-Size to 0.