Thanks for advice. It sounds good as you wrote it, but it does not work. I mean the part to find out where the connection was lost and restore it. Items remain grayed out and that is it. How do you restore the connection? Is there some secret DOS command, specifically invented by Adobe so that it cannot be intuitively used from the drop down menu by anyone without completed advanced learning course? I tried to re-import instead, but all pictures in folder are greyed out and import button is greyed out, too.
After more and more pictures from different folders were losing connections as I tried different things to restore it, I reinstalled the LR hoping that everything, including references to imported pics will be gone. It did not happen. Other importing editors before uninstalling ask if you want to keep pics references in case you change your mind. Adobe does not offer such choice. I made another unwarranted assumption that everything will be wiped out. It was not. But after reading advices like yours, I tried uninstall from inside the LR. That worked. After that I would not try to import the set for editing again. LR acts quite aggressively when importing. It would import not only the folder which I ask, but everything it can find on any connected device. Awful.
Luckily, the copy of LR 4.4 on my laptop with Win8.1 still recognized the folder and I was able to finish off the editing job. Well, Adobe had yet another surprise for me. When I “exported” the entire collection to JPEG using, just in case, two different Export commands, because there is no one simple “batch convert to JPEG, TIFF or whatever” command available, I found out that there were no edits included with any converted pictures. After two weeks and dozens of wasted hours I was exactly where I started. So I gave up and now I am half way through the folder again, for about the fifth time, but this time with the simple, straightforward DPP. I may not be getting results like with LR, especially with high/ low tones, but at least I know I am getting something rather than nothing.