I have a very extensive library on my iTunes and so have a selective choice of what I would like synced to my iPhone 6. After the first sync I get a list of over 108 tracks that couldn't be synced due to them not being able to be converted (even although other tracks from the same CD have converted and synced. Next day I re-sync and a number of those unable to be synced the day beforehand are synced but others are still left out. This goes on ad infinitum and it is driving me round the twist! Why do some tracks from a CD sync but others don't? And why do some tracks that can't be synced one day, sync the next? Is this some programmer with a warped sense of humour??