RPG's Side-View Battle System - A script error

[-MZ-]

Hello, I'm having a strange issue with the animated (enemy) battler for just one particular monster. He has the same dimensions as the other files, but whenever a battle starts with him in it I get this message:

Script SceneBattler4** line 406 error occured.

Undefined method 'frame_width' for nil:NilClass

Here's what line 406 is:

	   x += @spriteset.enemy_sprites[target.index].frame_width / 2

Here's here's the entire code:

Spoiler: Code

#==============================================================================
# ■ Scene_Battle (分割定義 4)
#------------------------------------------------------------------------------
# 　ãƒ