Is your Clip set, under System settings/USB mode, to MTP? MTP mode can do things like that. If you don’t need DRM capability, which MTP mode enables, I’d set the player to and use MSC mode–much less problematic.
Before doing this, though, transfer your content back to your PC (if you want to save it) and delete your content on your player (or simply reformat the player, under System settings), and then set the player to MSC mode and transfer your content to the player–hopefully, it now will transfer without any issue. And keep the player set to MSC mode.
