More information would be helpful

It would be helpful to know some more information. I was caught by your question because I had a problem just like yours once. The grey bars showed up in previews of the images in the photo application I was using. As it turned out, when I would view the actual image, it was OK. So, depending on whether you're looking at the actual image or a computer-generated preview, you might be OK.

Most likely, the issue stems from corruption of the data on your hard drive. If this affects more than just one or two pictures, it's not an issue with bad sectors that weren't identified, but actual data corruption.

You should do a thorough check of your hard disk to make sure there aren't any permanent issues.