So, I eliminated one thing at a time from the attempted backup from the Samsung SSD. I was attempting to backup c:\users\ken, which failed part-way through. When I eliminated c:\users\ken\appdata from the files to backup, all worked as usual. I have no idea why, but I suspect I don't need a backup of the appdata files anyway. More importantly the larger backups from my data hdd's work fine as usual.
Happy New Year,
Ken
Happy New Year,
Ken