My problem was in the writing...

I had the same problem just the other day--a large grey bar occupying about a third of the picture. I had just copied the jpg files from my SDHD camera card; pasted them to a folder on my computer. All were fine, except for this one picture. I went back to the card and copied/pasted the same picture again and all was well.

In my case the duplication process failed. I suspect the write-behind buffers were interrupted--I was in too much of a hurry. At any rate, the original picture was fine; it was the transfer process that caused the initial grey bars. A second copy attempt solved the problem.