The other major thing that comes to mind are ‘forbidden’ characters. Another user had a similar problem and it seemed they have a couple of characters that kept the file from being recognized.
I noticed that the Nubya files are .m4a. I’ve seen that people will sometimes have problems with some .m4a files being recognized and that seems to get fixed by transcoding them to another (similar) format like FLAC. I sort of doubt this is the problem you are having. If that was the problem, Nuwriy would have had a problem reading it too.