You can only take 500mA from USB - this is not enough to run the player and trickle charge the battery.

500mA is enough to trickle charge a mobile phone, which doesn't have to contend with impulse currents when a hard disk spins up. Even so many mobiles take more, but the USB charger manufacturers don't care about USB compliance.

FYI our other (smaller) new portables do take power from USB.

Rob