Failed again after reboot
Files canít be copied onto the backup disk because it is read-only. You may need to repair or erase the disk using Disk Utility. If the disk canít be repaired, select a different disk for backups.
Immediately, I used First Aid to check both the volume Time Machine and the actual drive. Both said no problems.
Going to leave the imac on and will see if backup fails again.
Edited by blfamily (Tue 21-May-19 06:58:02)