USB cable is about 1.5m/5ft long, but your point brings up another thought. I am connected through a USB hub and not directly to the laptop. Will plug straight into computer and see if issue remains.
Apparently this has nothing to do with transferring the file.
An image that had been on the hard disk for a while now just got damaged while zooming in. The result is a shown above. Could this be a damaged hard drive?
Almost certainly a hardware issue - this kind of problem is generally tracked down to a failing hard drive (that's what caused it for me), problems with RAM, or a something wrong with the card, the reader, or (if the images are being downloaded straight from camera) a USB cable fault, but that seems to be ruled out here.