My Passport Ultra: "Some files failed to backup."

Hellos.
I recently bought a My Passport Ultra on Amazon but when I try to backup my files for the first time using WD Backup, all I get is a notification that says “Some files failed to backup.” Yes I updated and restarted my computer after installation. Any help?

Hi, which are the files that where not backup? Sometimes if the system is using those files the software might not back them up.

Sorry, this is poor response. How do I know what files failed to backup?