I had some images in a folder. I realized I had to split them into 2 folders.
I created the new folder in LR. then I think I moved them in Explorer as I was still working and I needed to add a couple subfolders...
Since LR asks if I want to move selected to the new folder, which I didn't have, I moved them in WinExplorer or ACDSee as these are real files, not a overlay catalog.
So I thought I could sync things straight when back in LR.
But NOoooo! :-)
So now ther was a folder but it wont Sync or Import the images that belong within the folder.
I tried deleting the folder in LR to do it fresh. It sees the folder, and it still assumes they already exist. So I tried unchecking New photos or Dupes, and no luck. I tried from Add, to Move..No luck.