My iPod Touch won't play some of my files I've been having trouble with my iPod Touch. I mostly use it for listening to podcasts, however not only will some of the files not play, some aren't even accessible. Where files should be, there is simply an icon with a silver musical note on a white background.
If it's working now, it sounds like a software bug. I'd go ahead and update it iOS 6.1.6, the latest version that the 4th Gen iPod Touch supports.