When "Preview" is selected, the screen shot images for one of my sites are just blank rectangles, even though the pages are cached. Does anyone know what would cause this?
Note: Surprisingly, despite these blank images, so far the Google traffic for this site hasn't dropped significantly. This suggests that most searchers either don't use the "Preview" option, or else still click despite the blank images. Even so, I would still like to know what is causing the images to be blank.