Can't Battle or Receive Pokémon?

Assuming this is the error you’re getting

Try this first HELP! Game.exe has encountered a serious problem

If that fails and if you don’t mind missing out on some music, you could remove the ME folder, the issue is caused mainly .mid or .midi files.

Well, you can either remove the ME folder or you can replace the audio folder from here, another user converted them all to .wav files. (It’s probably better to run a scan on them first, because I don’t know anything about that user) A miraculous (?) solution to Mac’s mute music

For moving/deleting the ME folder, go to your game files, there should be a folder named ME within the Audio folder.