Thanks for your suggestion. Yep. Rebooting is always a good idea. I tried that quite a few times. I have also tried to plug into a different Windows PC altogether, and that one also reports that there are errors on my device and it also fails to repair them.
I just downloaded the latest firmware 1.2.1. The Nook was running it already, but I thought I'd try to update it anyway. After that was done, Windows reported the same error still, but I was able copy books to the device and read them.
This morning I can still read the books, but now windows doesn't register the Nook at all when I plug it in, regardless of which usb port I use. The Nook itself knows that it's plugged in. It switches to USB-mode and is charging.
As a side note: All my other USB-units are working. Mouse, Keyboard, WiFi-dongle, sketchpad, external harddisks, etc. Plugging the Nook into a different USB-port (e.g. one where a functining harddisk has it's normal place) doesn't change anything either.
It kind of bothers me, that the same exact thing happened at roughly the same time, when I performed the exact same operation (transferring files from Calibre). And it bothers me even more that I don't know what conclusion to draw from it.
