[Error] Game crashes when I battle a Rocket Grunt. How do I fix this?

[SuperSpyroDragon64]

Starting a battle with the NPC crashed the game with the error message pasted below, so I copied him and deleted everything except the "start battle" command. Talking to this NPC and starting a battle still crashes the game. He's just a rocket grunt and his only code is:

Conditional Branch: Script: TrainerBattle.start(:TEAMROCKET_M,"Grunt",1)
Else
Exit Event Processing
Branch End

This is the error message:

[Pokémon Essentials version 20.1]

[v20.1 Hotfixes 1.0.7]

Script error in event 11 (coords 6,6), map 22 (Pokémon League entrance)

Exception: NameError

Message: wrong constant name Battle::Move::

***Full script:

TrainerBattle.start(:TEAMROCKET_M,"Grunt",1)

Backtrace:

172:Battle_Move:58:in `const_defined?'

172:Battle_Move:58:in `from_pokemon_move'

161:Battler_Initialize:89:in `block in pbInitPokemon'

161:Battler_Initialize:88:in `each'

161:Battler_Initialize:88:in `each_with_index'

161:Battler_Initialize:88:in `pbInitPokemon'

267:ShadowPokemon_Other:196:in `pbInitPokemon'

161:Battler_Initialize:61:in `pbInitialize'

148:Battle_StartAndEnd:117:in `pbCreateBattler'

148:Battle_StartAndEnd:153:in `block (3 levels) in pbSetUpSides'

If it helps, "if Object.const_defined?(class_name)" is at Battle_Move line 58 and it looks fine to me. I don't see what could be causing the crash.

  # This is the code actually used to generate a Battle::Move object. The
  # object generated is a subclass of this one which depends on the move's
  # function code.
  def self.from_pokemon_move(battle, move)
    validate move => Pokemon::Move
    code = move.function_code || "None"
    if code[/^\d/]   # Begins with a digit
      class_name = sprintf("Battle::Move::Effect%s", code)
    else
      class_name = sprintf("Battle::Move::%s", code)
    end
    if Object.const_defined?(class_name)
      return Object.const_get(class_name).new(battle, move)
    end
    return Battle::Move::Unimplemented.new(battle, move)
  end

 

[SuperSpyroDragon64]

This doesn't happen when I swap the Grunt's 3 pokemon (Sandshrew, Rattata, Zubat) for a Voltorb.