Originally Posted by chaley
It means that some device connected to the computer has USB IDs that calibre recognizes, but that either no disk drive known by calibre to be associated with the device can be found or the disk drive cannot be written. This situation can arise because the device is non-standard, is new but reuses a previous USB ID, or has firmware changes that calibre doesn't know about. It can also happen if some device is presenting bogus USB IDs.
Thanks! I appreciate the explanation. Presumably the reason for the retry is in case the device simply hasn't finished initialising the USB connection, or something like that?