The error shows in which java method an error occured (the method on the top) and shows which other methods are affected by it. So you don't have to call all these update() functions. That's already done. If you start PZ via console.app you get the error message printed to your console. It shows another 2 rows then: Aug 20, 2013 2:15:22 PM zombie.gameStates.IngameState updateSEVERE: nulljava.lang.NullPointerException at zombie.iso.IsoChunk.update(IsoChunk.java:311) at zombie.iso.IsoChunkMap.update(IsoChunkMap.java:62) at zombie.iso.IsoCell.update(IsoCell.java:4803) at zombie.iso.IsoWorld.update(IsoWorld.java:1673) at zombie.gameStates.IngameState.update(IngameState.java:638) at zombie.gameStates.GameStateMachine.update(GameStateMachine.java:87) at zombie.GameWindow.logic(GameWindow.java:586) at zombie.GameWindow.run(GameWindow.java:980) at zombie.GameWindow.maina(GameWindow.java:856) at zombie.core.LaunchDialog.main(LaunchDialog.java:208)That means that an NullPointerException (basically a missing object/value) occured in zombie.iso.IsoChunk.update(), which is executed by zombie.iso.IsoChunkMap.update() and so on... I'm completely new to PZ modding, but I guess you have to set some other values on you current chunkMap to get the right chunk. I couldn't figure it out yet. Maybe analysing the spawn process of the player or zombies could help.