One alarming possibility (not sure if it would result in that error).
DRM-protected files are tied to you, who is the purchaser. If you authorise your computer
before you download the DRM-protected book, then Digital Editions will tie the book to
your Digital Editions account. You can authorise up to 6 different computers or devices
and copy your DRM-protected books between them. But if you did not authorise your
computer before you download the book, then Digital Editions will tie the book to your
specific computer. If you buy another computer later on, or even if you reinstall Digital
Editions again, you will not be able to access any books you have already downloaded.
So if you have not authorized FIRST, the books will be locked to a single device - OUCH!
Actually, it sounds more like a USB problem, does the port work ok with flash drives / pendrives.