Users of my plugin have been haunted by this error. http://pastebin.com/qvkuVjdz The lines of code mentioned in the error, can be found here: https://github.com/Bukkit/CraftBukkit/blob/master/src/main/java/net/minecraft/server/Container.java On line 253, and 418. It looks like the error happens because k = 1. Forever. Somebody found out how to reproduce the error. 1. Create a treasure container with my plugin. 2. Shift-click an item (error happens) It only happens when shift-clicking inside any container OTHER THAN chests. I don't know how my code can be responsible. I rely on bukkit's method getServer().createInventory, https://github.com/Mtihc/TreasureCh...easurechest/v8/core/TreasureManager.java#L344 and bukkit's serialization of ItemStacks. https://github.com/Mtihc/TreasureCh...t/treasurechest/v8/core/ItemStackWrapper.java Any idea's?