Help! TimeMachine on MAC tells me that it can't finish backing up to WD Passport Ultra

Hi! I am NOT GOOD AT ALL with computers, so probably I am doing something wrong. Basically, I have used the WD Passport Ultra to back up my Mac every months for years. I got a new MAC, though, and when I try to back up, I get an error message saying, “Time Machine did not finish backing up because some files were unavailable. Backups will resume when your MAC is unlocked.” Unlocked? I have never locked or unlocked my MAC while backing up. Maybe it’s because I am backing up a new MAC? What do I do guys?

Hi @JenniferP,

Please refer below link check Error: ‘Time Machine could not complete the backup.’ occurs when backing up to the Time Machine share:
https://support-en.wd.com/app/answers/detail/a_id/18982