Please state the version number of your Lightroom (go to Help->System Info)
Also, what happens if you connect the camera to the computer (and not use the card reader)? Does the import work then?
Yes and it made no difference
Version number is Lightroom version: CC 2015.10 [ 1111918 ]
I don't understand why this issue is occurring given i had no problems at all with previous versions of LR wirh OSX 10.12.4. Is there a bug in new LT version?
Would it be useful to uninstall and then reinstall LR. If I do this will presets and catalogs be automatically reinstalled?
I am not a fan of connecting camera to computer: too slow. But will try it.
Is the card reader accessible outside of Lightroom without any problems?
What going on when you copy the images on the local hard disk and then import to LR from this?
Is your system actually patched to the last versions (operating system, drivers, etc.)?