Can't add new tracks to existing playlists.

[Rj22]

Hi,
I have spotify on my iPhone 5, premium membership, up u til the last week or so all has worked fine but now I can't add any tracks to existing playlists. I can create a new playlist but once it's created I can't put any new tracks on it.

I have the latest iOS and the latest version of spotify and I've tried restarting the phone and re-installing spotify but still have the problem.

Anyone have any ideas?
Thanks for you help.
Rj22