Hi,
I was able to reproduce the problem, and it doesn’t look like it’s coming from a filename mismatch: in my case, the file A10-3.mp3 failed to play, and it looks like my browser never even sent a request to fetch it. PennController keeps only up to 4 pending requests in parallel, to prevent flooding distant servers with requests. It could be that sometimes, 4 audio files fail to fully preload, so PennController never gets to the remaining resources. In my experience, this is more likely to happen with Firefox (and when requests lots of resources) because of the way it loads media streams. I have updated the way that preloading is detected in PennController 2.1beta, so you could try overwriting the copy of PennController.js from your project’s Modules folder with it, and hopefully that should address the issue
Jeremy