Passport Essential 320mb not recognized by digital photo frame

We own a new ViewSonic 15" digital photo frame w/ working usb conn (it reads and opens usb flash drives we plug in). Our new Passport Essential is not recognized by the digital frame.

Passport Essential works fine on our computer - does everything as advertised, including viewing the same Jpg files we cannot access on the digital frame.

Any thoughts on what we are doing wrong?