I Transferred Yahoo! Music Unlimited Tracks to a Portable Device From Two Different Computers and Now Some Tracks Won't Play
Yahoo! Music Unlimited subscription tracks are tied to a single machine when it comes to transferring to a portable device. That means the system assigns a license to one computer for transfer. So, if you transfer some tracks from your computer at work, then you transfer more tracks from your laptop at home, you may find the first set of tracks transferred no longer plays on the portable device.
To avoid this overwriting of licenses, designate a single computer as your point of transfer, then be sure to manage your portable device from that designated machine.