I am getting this error much too often. I am copying a big number of files from a slow device (external hard drive) to my Mac. When the copy is completed, the last top folder is still marked as "incomplete".
I only managed to clear the mark by creating an empty folder with a different name (say "Folder2"), moving the contents of the folder (say "Folder") there, erasing the (now empty) folder "Folder" and renaming "Folder2". That all looks weird to me. Any suggestions?
Update: External drive is formatted in FAT32.