Nook HD+ won't read SD card - comes up with "SD card damaged. You may have to reformat it".
Cancel or Format - and then nothing happens..!
The HD+ has written off a CM10 card so badly that PC won't read it.
But the HD+ won't read a card that the PC will happily format.
Try to use a SanDisk 4X speed card.
Ideal is to format it using PC or Nook BEFORE using.
What OS do you have?
If you have Windows, then you can get lots of SD Card formatting software.