Hmmm, try this:
- Download the file here and make sure the name is: 'Oldale TownLavaridge Town (Pokémon Omega Ruby & Alpha Sapphire OST)'
- Without the quotation marks!
- And put that in the bgm folder in the game.
- I think it might be a problem due to the é in pokemon and your keyboard/language of your PC not picking up on it.
Hope it helps!