I had a case where a slight change on payment method at bn klutzed the tools (I just updated the card expiration date). I had to reinstall Nook for PC, then all was well again. I'm not sure if this would work for Nook Study, too, but it's worth a try.
On the subject of what type Nooks have proper file access (no rooting required) - I have a Nook Color, and it's just a matter of plugging it into your PC with a USB cable. Drag & drop files. Presuming a similar process would work on Macs. Notably - to get true magazine view with pictures, I have to go through the NC device on the way to Calibre. NOT Nook for PC. Nook for PC only delivers text. Since I subscribe to National Geographic specifically FOR the pictures, this is not acceptable. If you care about such things, consider picking up a used NC.
Finally - if you are (quite justifiably) worried about battery life on these old devices, check out
www.newpower99.com I replaced the battery on my Subaru-specific TomTom. Easy directions & tools to do it. They have a battery for my NC when the time comes. Highly recommended. (For the record - my only connection with them is happy customer.)
