For all users having issues with writing songs, I too thought the game was glitched with this, however it turns out that writing a song is an extremely painful ordeal, it takes roughly 15 sim hours to produce each song, a couple of helpful hints, when you start writing a song and then have to carry on with your day, when you come back to continue, don't make the mistake of using the intrument, otherwise you'll end up with multiple copies of the same song, go to your inventory, they are listed as "sheet music" resume from there, otherwise you'll have multiple copies of the same song at various stages of development and they cannot be sold or deleted (as far as I'm aware). Also for those who are experiencing the glitch where you quit the action but it continues regardless I have found a work around; After quitting the action, qeue another nearby action, and this will quit the songwriting. I hope this helps all you simfanatics out there.
Chris.