Okay.  So.  Someone very helpfully pointed out to me something that I... somehow entirely missed right at the beginning of the game.

So far as I'm aware, this doesn't prevent you from playing the game... however, there is the fact that it's annoying as all hell.  So!  Let's walk through how to fix this.

In the game folder, you should see three subfolders.  These should be "locales", "swiftshader", and "www".

First, open up the www folder.  In there, there should be other folders, where the game's main files are stored.  Now open up the one at the very top, named "audio".  From there, open up the top folder there, the "bgm" folder.

Now just download the "Version Rin music error fix" file and slap it in there.  It SHOULD be the necessary music track, and it'll stop the error from popping up.