Originally Posted by viperboy
download a free eTextbook and use Calibre to convert it to ePub.
Can this converted epub be viewed by the built-in calibre viewer?
How about an epub editor like Sigil? Perhaps, resaving it using Sigil may help it display.
I usually use the ADE pc viewer as my ultimate .epub compatibility tester...
should I maybe use a different reader/format?
So if it works outside of the nook app, then perhaps it needs to be tweaked to work there, but you could also try Aldiko, cool reader or Moon+ reader available from the Market. On my TF I usually use the nook app, but version 2.5 (not the latest as it crashes too much on HC). On my rooted NC (GB ver. 2.3), I do use the latest nook app (version 2.6.2) and it works quite well on virtually all of my epub's.
You could try converting the original ebook to .prc/.mobi first using calibre, then used FBReader for android to read it.
Or perhaps re-convert that converted .prc ebook to .epub again using calibre and try that new one in the nook app.