You need paid account, Web or Unlimited but I'm not sure which. Do you have paid account? I cannot test this because I don't have paid account and I'm not going to pay for both Spotify and Rdio.
Yes I've got an Rdio Unlimited subscription. Mobile playback works which means that the sub is in place and it was working when you first added the functionality.
Let me know if you want to do a screen sharing session or to get an account.