Can't transfer some .MOV files
I'm transferring files from one of my iMacs to an external hard drive. Things were going well, but I began having trouble with certain .MOV files.
The problem files have the same number as files that transfer smoothly, but with a suffix. Often the icon to the left of the problem file's number is a dark rectangle, the icon on those that transfer smoothly is like a miniature page with a corner turned down and what looks like a blue letter Q over it.
ex: IMG_4897.MOV 9 KB QT movie
IMG_4897 2.MOV 24.3 KB QT movie
The error message says: The Finder can't complete the operation because some data in "IMG_4897 2.MOV" can't be read or written (Error code -36)
What adds to the annoyance is that if I attempt to move a group of files at one time, the problem pops up with the second file and none of the following files will move — I can move just one file at a time, and I have MANY !
iMac, macOS 10.12