I have had a Sony PRS 650 which just died, and I bought a Nook Glow, as it is the only one with a light. I had been using Calibre to load books to the Sony in epub format. I brought home my Glow, told Calibre that is what I have (at least I think I did), left the format as epub (and most of the books were purchased from various places as epubs anyway) and loaded my books onto the memory card. I open my files on the Nook and try to open one of the books and am told "The NOOK cannot read this file. It may be an unsupported format." It does show in the list of files as epub... I don't know what I'm doing wrong. Can anyone help?