I had this error after a rebuild of my office computer where I do my photo editing in Lightroom 6: “Lightroom has encountered problems reading this photo”. It wasn’t on all pictures, just some of my most recent shoots. After some searching and troubleshooting using my two favorite search engines, I was still drawing a blank as nothing was working. Cutting to the chase, I needed to grab the latest Lightroom 6 update (6.14, at the time.)
When I rebuilt my computer, I used the Lightroom 6 installer I had lying around. Since it was an older version, it didn’t know how to read the photos that had been edited with the newer version of LR6. Seems obvious in retrospect, but I wanted to post the solution here in case it helps anyone else as the error message isn’t all that helpful in troubleshooting.