.SDR folders empty when loading MOBI covers on Kindle Paperwhite

Hi all,

I just got a new Kindle Paperwhite, and I'm trying to get the covers to show up on the list screen. I've had success with one book so far, here are the steps I took using Calibre (steps 1-5) and Mobi Meta Editor (steps 6-7) from a previous thread to get it working:

"Here are the steps I took.
1) Choose the book and select Convert books
2) Change output to Mobi.
3) Go to Mobi Output and make sure 'Personal Doc tag' is [EBOK]
4) Make sure Enable sharing is turned OFF
5) Click OK to convert the file.
6) Open the file using MobiMetaEditor
7) Change 113 (ASIN) to be the ASIN of the book from Amazon. (Preferably the Kindle Edition's ASIN)
8) Save the new mobi file and copy to Kindle."

So this worked for my first book, but hasn't worked for the second - it just shows up as the name of the book with the default art for coverless books. As far as I can tell, the only difference is that the .sdr file contains a .mbp1 and .mbs file for the working book, but it is empty for the non-working one. I've tried deleting the old .sdr folders and MOBI files, in both batches and single books, but I can't seem to get it to update the .sdr files.