The usual cause of this, is that the Photo Filename was entered in the .CSV incorrectly but the photo itself was correct or the Photo File name is entered Correctly in the File and is incorrect within the Photo.

Some Examples:
  • If the file name in the File is 12345L and in the photo name is 12345
  • If it is Capitalized in the photo name but not in the File
 
Once you change the filename of the photo to match the name on the CSV File, or change the name in the CSV File to match the Photo Name, it will upload successfully.