Whenever i attack an npc the server cmd gets filled with this:

Code:
java.lang.ArrayIndexOutOfBoundsException: -1
        at NPCHandler.AttackPlayer(NPCHandler.java:708)
        at NPCHandler.process(NPCHandler.java:2525)
        at process.run(process.java:25)
        at java.lang.Thread.run(Unknown Source)
java.lang.ArrayIndexOutOfBoundsException: -1
        at NPCHandler.AttackPlayer(NPCHandler.java:708)
        at NPCHandler.process(NPCHandler.java:2525)
        at process.run(process.java:25)
        at java.lang.Thread.run(Unknown Source)
Any ideas?