Thanks for the advice! I have mp3 files for music, and WAV files for voices. Bizarre experience building this little, 3 level platformer! Built for Windows - no problem. When I tried to do an online build, I kept getting that error, and assumed that the build process stopped there. So I kept retrying, in case it was my crappy, third world internet. Well, when I eventually happened to look in “my builds”, there was a shitload of them building there! So the problem wasn’t preventing them from building after all. Unfortunately, however, there is always an error in the build - the music is missing from the first level.