Now I have an additional question. I wasn't able to use the original update file from Google, presumably because I had deleted the Google Books app. I kept getting the above-mentioned error.
Just out of curiosity, how could I get Google Books back so the update would run? Just placing it in /system/app didn't seem to work.
Not that it really matters, I used the modified update file that danger-rat posted, but for the future I would like to know how I can avoid this error.