Lightroom Classic suddenly does not import my photos

I have been a Classic customer for years and imported thousands of photos from my Mac computer or directly from my Nikon D750 .... until now.  My new photos show up on the screen for my selection, but when I click import the screen goes blank.  When I after many minutes of nothing close out the import request I am shown one of two messages:

 

"the following files were not imported because they cou...ot be read or the destination folder is not writable. (97)....or...the same message with (191) 

 

I am doing nothing different than I have before.  What could have happened and how does the program get back to working and allowing me import.