Originally Posted by jnorth
Shooting at the wrong time of day for the location, or basically a generally wrong time of day - noon. To get the falls and other highlights within only 4- stops of being beyond blown the area the line was in was deep deep shadow. Haven't ever noticed a horizontal segment before and not in any other shots taken the same time either before or after this one. I'm not sure if it is an exposure issue, or something else, perhaps a bump of the camera while it was writing the image, though if it was a bump I'm sure I woulda noticed this a few times before now.
full image crop showing the line
OK, this is either a bad sector on the card, a faulty card reader or a faulty graphics adapter on your PC.
If the first, the original file will appear the same on another computer using any card reader but using the original card.
If the second, it will be OK if you just use a different card reader with the original computer and card.
If the third, it will be OK on any other computer using the original card and card reader.
Good luck!