Hey Bro, just to clarify, did this error occur when you installed BattleEffects or AnimationX?
This error code isn't produced by my plugins, and the log states it's a conflict with VisuMZ_1_BattleCore.
Please confirm which plugin exhibited this behavior and at what stage of the test it happened, and I'll do my best to work around the problem.
Everything indicates it's a compatibility issue due to two plugins using the same class or manipulating the same object (perhaps the damage popup).
Please confirm these points, and we'll investigate and resolve it.