Calibre & Samsung Nook Tab E

I've been using Calibre to load a Nook HD for ages now, but sadly, our Nook died -- just in time for the trade-up at Barnes and Noble. So, yay! we could trade in our deceased Nook for a discount on a Samsung Nook Tab E (yes, we're thinking, the bigger, the badder!).

For years, I've been able to transfer books from Calibre to the Nook HD. This has been great, since one of us reads on a Kobo, and one on a Nook. However, this new Samsung/Nook has me stymied.

When I connect to my PD and launch Calibre, it sees a number of books already there on MAIN device, BUT!!! they're not there! I suspect they were on the old, deceased Nook HD, but I'm not 100% sure of that.

At any rate, I have found that I'm having trouble transferring books from Calibre to this new Nook. It seems to be seeing a device that is no longer there, and even when I send to device, NOTHING GOES ONTO THE NEW NOOK.

Any help GREATLY appreciated.