I'm having trouble with about 1/2 the covers not displaying properly on my Sony PRS-350. Instead of the cover graphic, it's a plain white page with the title and author.
The Calibre Library has correct covers for every book. If it didn't, I loaded my own cover through edit metadata. Then I plug in the device, upload to device, but still about 1/2 of them show the plain white text page only. I tried deleting the books from the 350, and noticed that the thumbnail image remains so I manually removed any leftover. Then sent the books to the device again, and same thing happens with same books, the thumbnail is the plain white text page. It doesn't matter if I send multiple or single books at a time.
I changed Metadata management in Preferences to Automatic management, and that didn't help at all. I tried resizing the original images thinking they were too narrow and when they were turned into thumbnails, the size was causing the problem, but that didn't work either.
What I finally did was to just edit the thumbnails directly on the Sony using my original color image and resizing it to 168x217 in greyscale.
Although I really don't mind doing the edits manually, I'd prefer the program do it correctly in the first place but can't figure out what I'm doing wrong. I'm using the newest Calibre, 0.7.43.