Time Machine
In trying to use a new external drive for Time Machine backup, I got a message that Time Machine needs to erase a Seagate drive in order to use it for backups. I clicked OK to erase, which was performed, but that got an error message "There was an error preparing the Time Machine backup disk “Backup 6. Couldn't unmount disk”. I manually erased the disk but I still get the error message, and am stuck at this place. Time Machine won't permit the new drive to be used for back up. Suggestions? Thank you!
MacBook Pro 15″, macOS 10.13