Don't know happened there, maybe it is because of the beta version which contains bugs, the download incomplete, or extraction incomplete? The audio file should be there, I had the previous 4 versions which all contains the audio file.
Anyway, the Public version was released earlier today, you can try that even the compressed version should be fine. It was no longer beta and all the game breaking bugs should have been fixed.
Edit:
I just now downloaded and extracted the Public Release v0.13a and just by quick look, the audio file is indeed missing, perhaps it is replaced by another but the beta code still refers to it. I will have to check further.
I had the same error as well, just downloaded it yesterday. I have a rpaextract program and I extracted the audio.rpa file, saw the file wasn't in their, copied one of the other files and just named it "blue sizzle.mp3" in the folder and now it works. All that code is doing is looking for any file named "blue sizzle.mp3" to play. Anyways, it's working now but playing the wrong music, but... meh lol.
An alternative would be... go to the game/scripts/ folder and edit the day1.rpy, basement.rpy, and day5.rpy (the missing track is referenced in these other files as well) files with notepad and replace the text "blue sizzle" with "hush" (hush is one of the tracks currently in the audio folder), and it should work.
I've included the modified files below if you don't want to go through the trouble of editing them yourself, just drop them in the folder and they "should" work. I'm a Python dev, so theoretically it should work, but know nothing of renpy, so use at your own risk. It's working for me right now at least. "
But for smaller games it may be if they don't know there was an update because it wasn't on the LU page. 
