Odd issue dragging to Lightroom

[JAS Photo]

I'm trying to Import some older image files into LR (CC) - I've done a few folders no problem - then I try to drag this folders images (red, Yellow or Green) to LR the folder show up with no images in it. no images to import. BUT if I drag them for windows explorer the get imported to LR. Any Ideas?

[JAS Photo]

Figured it out - They were already in the catalogue but still shown on an failed HD that was replaced (drive letter changed) - Still don't understand why difference between importing from windows & PM.