Time Machine states Backup not complete
I am running Mac OS Sonoma. I have a WD 2TB external jd. I formatted it according to Apple instructions. My first backup was successful. When I logged in to my Mac pro this morning, I received the following message "Time Machine couldn’t complete the backup to “Time Machine”
“/Volumes/Macintosh HD/boot/x86_64SURamDisk.dmg” could not be backed up.
I don't get how it could back up the first day but not the second. How can I fix this? This has happened time and time again but never pursued it. Can anyone give me a corrective action?
Mac Pro (2019)