When I use the browse button in the preferences to set the path to the library, the usb drive is not listed. I can only see the local file system. The same thing happens when I go to add a book that is stored on the usb drive to the local Calibre library, the window opens showing the file system but the usb drive is not listed there, only the folders on the local drive show up. I have been unable to get Calibre to recognize the existance of usb drive at all. The drive is mounted and active to the operating system and other programs.