I just purchased a new iPhone 6S from Verizon for my wife and I inherited her old iPhone 6. Verizon transferred everything from the old 6 to the 6S and wiped the old 6 so that I could set it up fresh. Both phones work great except I am unable to sync from USB iTunes to the old iPhone 6 (Wireless sync does not work either). Sync does work OK with the new 6S. My MacBook Pro is at 10.12.3 with iTunes version 188.8.131.52. The iPhone 6 IOS is 10.3.1 and the iPhone 6S is version 10.2.1. Itunes recognizes both iPhones when they are connected and I can see and select those files I wish to sync but the window that allows me to select "All Files" or "Selected Files" is greyed out and I am unable to select either. I am particularly trying to copy a new ringtone I created but even other selections do not work. When I force a manual sync, it rapidly displays three steps in the status window but they are too quick to read and it never gives any error message. NOTHING gets transferred to my iPhone 6. When I repeat the same process with my wife's iPhone 6S everything works fine. I have searched the web for solutions to this issue but have been unsuccessful. Any help would be appreciated.