If you have used different pendrives and 2GB ones also, you can safely assume something to be wrong with your HU, especially the USB Port. If it is under warranty, you can fix an appointment with your JVC Dealer or else show the unit to the aftermarket guys.
According to the product page (Double-DIN AV Receiver - KW-AV60 - Introduction
), it doesn't mention about the size of the pendrive supported. But, at this price point, I am sure that 2GB pendrives are certain to be recognised.
Did you try playing music from the same pendrives?
Are you able to play videos through any other source?
Was the HU playing videos earlier and stopped all of a sudden?
Lastly, it may seem very stupid, but are you sure that the HU is capable of playing videos via pendrive?
Gurus can also help!