Scene_Battle problems

[Lestat]

Hi.

Every time I enter battle I get the error in the picture attached to this post.
When I look it up, this is on that line:

      "$game_troop.setup_battle_event"

I'm using Reedo's Simple Side Battle System and Yanfly Engine Zealous - Battle Engine Zealous.
I've tried removing them, replacing the "scene_battle" script with an original one... keep getting the same error.
I really haven't a clue on how to solve this.

Thx.