Perhaps the drive is asleep? Or the photos or folders or drive has been renamed or moved?
Anyway, once you find the location of your photos using Finder, you have to point Lightroom to this location using these instructions: Adobe Lightroom - Find moved or missing files and folders
<<< Perhaps the drive is asleep? >>>
The Finder located them (so the drive was working just fine), no problem, BUT if I used the built in locate missing files/images of LR, it could not find them -- it is as if they did not exist from LR's perspective. Tried the LR synchronize function -- no luck.
And this is not like I am new to LR -- been using it since version one, and I'm a software developer (retired). Even shutdown everything when it got late, and had the same problem the next morning. Somehow going off and testing LR with some other images in a different folder did something so that all of the "!" in the upper right corner disappeared when I came back to the "lost" images, allowing me to go into the develop mode.
Strange indeed and I'll probably never see it again...
BUT if I used the built in locate missing files/images of LR, it could not find them
That's not what the command does. it find them in the Lightroom Library. It does not find them in your operating system and reconnect them in Lightroom. Nor will Synchronize fix the problem of missing photos in Lightroom.
As I said above in my earlier post, YOU must find the photo location in your operating system (Lightroom will not do this). Since you had Finder find the photos, you know where they are, so the next step is to tell Lightroom to reconnect. I provided instructions on how to do this. Please give it a try.
Sorry that I was not clear. This is something that HAD happened -- something that just fixed itself. I'm wondering what MAY have happened.
When I clicked on the "!", it told me the last place the image was located *and* that is where Finder said the image was STILL located there -- the images had never moved -- but Lightroom was unable to connect with the image(s).
The short description is that I was working on the images, went to Library mode, selected another image in Grid, went back to Develop mode and the message appeared that the image could not be found (forgot the exact wording). Worried, I shut down Lightroom, went to Finder and the images were still where they were suppose to be. The images were never moved, but Lightroom could not connect to them -- that is the mystery.
The next day after looking at some other images from a different "shoot" and going back the the "lost" images, they were all "connected". This is something that HAD happened and fixed itself.