Maybe Yamaha is waking up and not allowing all this transferring and cross sharing to the Sx900 anymore...?
Thanks Donny, no I don't think its that. I eventually got the pack to load after continually trying it, some work fine but some need a few tries. I'm not sure if it's a faulty pen drive I'm using (although it's brand new), or if it's too high in storage (only 64gb), a bug, or a blip.