I'm having exactly the same error updating my AVIC6100-NEX. I have a bag of USBs that threw off the error. I have double checked it is trying USB1. I have edited my registry to avoid t he creation of the folder "System Volume Information" that normally happens with all any USB on a standard Windows machine.
The Pioneer support person said basically, "I did it and it worked for me, your problem." I am stuck. I really want this update to 1.11 because it is supposed to help CarPlay. Any other ideas?