provoction error

[Doom]

System.NullReferenceException: Object reference not set to an instance of an object.
at Server.Items.BaseInstrument.GetBaseDifficulty(Mobile targ) in D:\DoomsDayUpdateFinal\Scripts\Items\Equipment\Instruments\BaseInstrument.cs:line 380
at Server.Items.BaseInstrument.GetDifficultyFor(Mobile targ) in D:\DoomsDayUpdateFinal\Scripts\Items\Equipment\Instruments\BaseInstrument.cs:line 416
at Server.SkillHandlers.Provocation.InternalSecondTarget.OnTarget(Mobile from, Object targeted) in D:\DoomsDayUpdateFinal\Scripts\Skills\Provocation.cs:line 127
at Server.Targeting.Target.Invoke(Mobile from, Object targeted) in D:\DoomsDayUpdateFinal\Server\Targeting\Target.cs:line 272
at Server.Mobiles.BaseCreature.DoProvoke() in D:\DoomsDayUpdateFinal\Scripts\Mobiles\Normal\BaseCreature.cs:line 8010
at Server.Mobiles.BaseCreature.OnThink() in D:\DoomsDayUpdateFinal\Scripts\Mobiles\Normal\BaseCreature.cs:line 8364
at Server.Mobiles.BaseAI.AITimer.OnTick() in D:\DoomsDayUpdateFinal\Scripts\Mobiles\AI\BaseAI.cs:line 3086
at Server.Timer.Slice() in D:\DoomsDayUpdateFinal\Server\Timer.cs:line 409
at Server.Core.Main(String[] args) in D:\DoomsDayUpdateFinal\Server\Main.cs:line 673