I have been saving several folders that contain some of my best photos to an external hard drive, and an X shows at the left top corner of several of the folders in the external hard drive. If I open these folders to look at the photos inside it seems that all are fine, but I have no idea what the "X" means. I searched on the internet trying to figure what the problem is, but was unsuccessful. Does anybody know what the X means? Thank you in advance for your response (s).