[DNSB]

Looking at the error message, it appears that your Nook may be using PTP (Picture Transfer Protocol) and not MTP (Media Transfer Protocol). This can cause some odd errors when trying file system operations other than simply copying/deleting files. If you are using MTP, you might want to try power cycling both the computer and the tablet.

The last time I played with a Nook tablet, I seem to remember having to swipe down the screen to see the notifications and change USB for charging mode to MTP. I don't know if this is still necessary.

Another question is what type of computer are you connecting your Nook tablet to. I seem to remember at one time, that to use MTP on a Mac, you needed to install a Google add-in though there's also an equally vague memory that calibre added an internal MTP driver.