P: Import Error "files could not be read"

This error message is typical of a permission problem with the destination folder to which you are copying your image.  Using your OS's tools verify that your User ID has read/write permissions on the folder where the images will ultimately end up.  

Correct: this is beyond me. I Assume of course that you habitually view your jpegs in Safari prior to Lr import and that you have never had this problem before. I'm no Apple fan, so I would not know whether or not Safari leaves dirty footprints in files.

Example: I used to work with Nikon software. Around 2011, a (fortunately shortlived) version of their import and conversion software ViewNX2 did that and I'm still having to throw away pics from that period because of suddenly appearing random color banding.

I hope someone can help you.

Thanks JaapV, 

Yes all the intended imports were jpg files, produced by the same camera (my iPhone), and there were no other intervening software (apart from safari open). 

I have had no problems with importing in the past and I haven't changed anything recently, except the update. I'm as confused as you may be! 

I have no cure immediately available, but I'm curious: were all the intended imports
1) jpg files,
2) produced by the same camera,
3) with no other intervening software?
(Just to exclude possible perpetrators outside Lr)