That means that album is not available anywhere. It looks like that artist may need to be merged with spotify:artist:4AK6F7OLvEQ5QYCBNiQWHq. I have just reported that to the content team.
If you try http://ws.spotify.com/lookup/1/?uri=spotify:artist:4AK6F7OLvEQ5QYCBNiQWHq&extras=album it should work just fine.