Right. So I've been trawling these forums for weeks trying to find an answer to this. 

I'm a premium user and have found recently that I am unable to play certain songs on my spotify. I just get a blank slider, the song doesnt start playing at all. Then, recently I found that most if not all of my songs started to play on my macbook but still don't work on my iphone. I have tried syncing, but nothing has changed.

I have followed all the advice given, getting the latest quicktime, (I have a macbook, so the latest quicktime is installed automatically) deleting local files, restarting spotify, logging out of Spotify. Nothing works. I don't really want to reinstall Spotify as I'll lose all my playlists which took weeks to create. 

What can I do to solve this? I'm getting so pissed off with it tbh, I would have left the service instantly had it not taken so long to create my playlists.