I also had this happen when I was messing around w/ the Novel and updating the firmware using a SD card, it also had the exclamation mark, but mine wouldn't fully boot up afterwards (kept getting the 'forcibly close' button instead of loading to the bookshelf).
I'm not keen on opening up the back of the PDN, so I tried the following: I connected PDN to my computer and updated the hardware using the PC method--problem fixed. Since the PC update was actually an older version, I then updated again using the SD card. This worked for me.
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