I have the same problem. Any solution yet?
It's possible the files showing in the explorer are in pdf format which is not supported in the organizer in recent organizer versions.
In that case, you can 'open' them in the editor and save them in any other format to be managed in the organizer.
Is it exactly the same exact message?
Thanks for looking into this. All my files are jpg's. I solved my problem by upgrading to PSE 2020 from 2018. Oh well, it's only money!
I know this was an issue a long time ago for you, but I'd still like to post here to save someone else the 8 hours that I spent trying to figure out Reconnect Missing Files.
I'm not enough of an expert to tell you how to fix the issue. But I can tell you how to prevent it in the future. When you move photos from a phone or camera onto a PC, always move them into the same folder. I have a folder called "Temp Photos". Once the photos are in that folder, import them into the Organizer with the keyboard shortcut Control+Shift+G
All of the photos open into Elements after you've approved this step using the usual dialogue box. Don't move. Freeze. Stay calm. Now click on each of the photos to assign Albums if you do that sort of thing.
Don't leave again. Now select File/Move and choose which Windows folder to store the photos on a permanent basis. In other words, let the Organizer move the photos from the Temp folder into your favorite windows folder for your photos. Once you've moved all of the photos, your Temp Photos folder should be empty. Open it to make sure.
Assuming it's empty, then choose File/Reconnect Missing Files to make sure everything went well. I've had so many problems with this aspect of the program back in the day that I insecurely "Reconnect Missing Files" everytime I open the Organizer, even if I'm not importing photos. I do this because if you catch a Missing File issue early, it's easy to fix. If you don't catch it for a few months, you're doomed if you're not well versed in nine different programming languages and have a degree from Cal Tech in computer science. In fact, I even think those folks would be doomed!