Failure to backup files

Why did WD fail to back up a few of my movie files (.mov and ,avi) yet backed up other movies  with the same file formats? No reason was given in spite of having plenty of disc space and while successfully backing others…Thanks, Jack

Hey there, If you used a software, try backuop the files manually by copy-paste / drag-drop the files to the drive, if that works, try updating the software. If is the WD Smartware, 1.-Uninstall the software, 2.-reset the computer, 3.- download and install the latest version and this should take care of it. I found software download and instructions are available on the link below.