Having trouble with undefined methods?

[brainstorm]

Having Trouble with the code below... on this line:

@spriteset.battler(@nv4).setmove(@nv3.display_x - offset, @nv3.display_y + 1, @nv4.screen_z)

It's saying undefined method '-' for nilclass.... But offset and @spriteset.enemy_sprites[0].display_x are defined.... so what's the problem...

Spoiler: Code

@nv3 = @spriteset.enemy_sprites[0]
    @nv4 = $game_troop.enemies[0]
    if @nv3 != nil
      @nv3 = @spriteset.enemy_sprites[0]
      @nv4 = $game_troop.enemies[0]
      offset = offset_value(@nv4)  
      if @spriteset.battler(@nv3) != nil
        @nv3 = @spriteset.enemy_sprites[0]
        @nv4 = $game_troop.enemies[0]
        @battler = @nv4
        @spriteset.battler(@nv4).setmove(@nv3.display_x - offset, @nv3.display_y + 1, @nv4.screen_z)
        @spriteset.battler(@nv4).setmove(@nv3.display_x + offset, @nv3.display_y - 1, @nv4.screen_z)
        @spriteset.battler(@nv4).setmove(@nv3.display_x + 1, @nv3.display_y - offset, @nv4.screen_z)
        @spriteset.battler(@nv4).setmove(@nv3.display_x - 1, @nv3.display_y + offset2, @nv4.screen_z)
      end
    end