Tom (and Richard) -thanks so much. This suggestion fixed the problem for me. I was trying to copy files from an old HDD to a new one. It would start the transfer and then stop with this error.
The old HDD (a powered one) was plugged into a USB3 slot on the top of my tower. After reading Tom's post I ejected it and plugged it into a USB3 slot at the back of the machine and now the data transfers without error!