Lightroom 6.0: raw files unreadable on Windows, my Mac reads them just fine

Similar to https://feedback.photoshop.com/photoshop_family/topics/unable_to_read_card_or_import_pics_on_a_mac .

I have a MacBook running OS10.12.6, and Lightroom 6.0 with CameraRaw 9.0. I recently bought a new Nikon 5600, upgrading from my 5100, and a new card to go with it.

I have successfully used this setup in the past to import photos from the card into Lightroom and manipulate them. When I went to do this today, however, I received the message "The files are not recognized by the RAW file support in Lightroom." I copied the files to my hard drive using the Finder, but get the same message on trying an import from there.

I've tried clearing my Raw cache, to no effect. The RAW files preview fine on my Mac, and they can be opened (albeit with some errors) in GIMP.

Never had a similar problem with Lightroom 4, and as I said, the existing setup worked fine for a while. Please help.