It could be in the song name, there seams to be a problem with spaces and certain characters so the best it just to call it 'song.mp3', upload it and re-name the song afterwards, it's changed to a number anyway on the server, song name, author etc are stored somewhere else, I think!

There's also the whole 'empty catch', re-boot, have a cup of tea, try again procedure!

Sometimes giving these things time works best,    I've had this one and the 'not valid mp3'!!!!!