Time machine backup not completed Message
For the past few months I am having problems with my external drive I use for Time Machine. I will click on TimeMachine and select backup now. I generally leave my Mac alone and when I come back I receive the following messages. Time Machine couldn't back up to "Time Machine MacBook Pro". I then click on that message and get "An error occurred while preparing the backup."
The backup disk is an external sandisk passport the I've use repeatedly. I have deleted old files and am at a loss. The disk has a USB that I plug into an Anker adapter. I've been having this problem for a few months, but usually after 2 or 3 tries it completes the back up.
MacBook Pro 16″, macOS 12.1