Once in a while, when we are doing maintenance, it is is possible for a user's plug-in to get unsynchronized with our server. This can happen only if you are actually downloading files during the short maintenance period.

The symptom of this is that the NR book files seem to open normally, but all the pages are blank. This is not the same as a blank window in your browser: You'll be able to scroll through multiple pages, and you'll see their boundaries, but they will be all blank.

Luckily there is an easy fix: Go to My Computer, C:, Documents and Settings, <your user name>, Application Data, FileOpen. You'll see a folder named NumericalRecipes. Delete it. Now, data will be re-fetched (and the folder reconstructed) as you open any NR book files, both ones already on your machine or newly download.