It is a somewhat erratic behavior. Sometimes I plug my Kobo in and Windows correctly recognizes it, I can explore directories and everything. Other times I get the "USB device not recognized" message.
My specifics: Kobo Glo HD, memory 2GB of 3.2GB, Nickel v.4.7.10413, Koreader v.2015.11, KSM 08, Windows 10, Calibre 3.16.0, Obok v.6.5.4.
As an example: today I plugged the Kobo in, and I could see it regularly, also inside Calibre, with all its content. After about half an hour with the device connected (no tasks), my Kobo suddendly disconnects. Calbre message is the following:
At this point, in the "Device and Printer" section I see the Kobo as an Unknown USB device (Port reset failed).
After rebooting the PC Windows allowed me to connect my Kobo again, and requested the scanning and repairing of the unit, which I did successfully.
When the Kobo was connected I tested it with the Kobo Utilities plugin in Calibre (Check the device database) and the answer was:
Anyway I have only about 20 books in Nickel and about 3 times that in a different directory to be read with Koreader. So not an heavy database problem
I would prefer not to restore the unit. All suggestions are most welcome