Lightroom Classic CC 7.5 and 8.0 will not import some AVI files. Windows 10 version 1803.

Earlier today I was running 7.5 and it would not import any AVI files. 
Message says

Could not move a file to the destination folder because it is not writeable or there is not enough free space

Well, that is just silly.  It is obviously writeable as Lr had just moved 120 jpg files that were in the same folder from which I was importing.
There is more than enough free space - 120GB free, and the files totalled a few hundred MB.

Searching through the Lr forum, I tried the clear video cache.  Surprisingly, I was then able to transfer some files. 
These were from a folder onmy desktop to a folder within My Pictures.

But not all.  The ones from my trail camera wouldn't transfer despite restarting Lr, and clearing cache.

Then I updated to Lr 8.0, becasue it said it fixed some bugs.  Perhaps I would be lucky.
I transferred the jpg files from the Trail cam but it would not transfer the AVI files. 
Clear cache. No change.
Close and reopen.  Clear cache. Increase to 5GB.
Lr finally imported 12 AVI files, but won't import two of the files.  This is from the Apeman H70 trailcam (USB 2 connection, makes it appear to be a thumb drive) to a folder within My Pictures.
Still the same stupid message.


Looking in the forum, the importing of AVI files seems to be a particular and recurring problem with Lightroom.

Once imported, at least mine seems to be able to play the files, unlike many of the other posters.