java.lang.NoSuchMethodError: net.sf.l2j.gameserver.model.L2MonsterInstance.getKnownPlayers()Lnet/sf/l2j/util/L2ObjectHashSet;
        at net.sf.l2j.gameserver.model.L2MonsterInstance.removeKnownObject(L2MonsterInstance.java:88)
        at net.sf.l2j.gameserver.model.L2World.removeVisibleObject(L2World.java:454)
        at net.sf.l2j.gameserver.model.L2Object.decayMe(L2Object.java:410)
        at net.sf.l2j.gameserver.model.L2Character.onDecay(L2Character.java:468)
        at net.sf.l2j.gameserver.model.L2NpcInstance.onDecay(L2NpcInstance.java:555)
        at net.sf.l2j.gameserver.model.L2Character$DecayTask.run(L2Character.java:299)
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
        at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
        at java.util.concurrent.FutureTask.run(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)