Yes - moving between two external drives.
I misremembered when I wrote the title: it was error 50, not 51. I also thought that I was dealing with MS DOS FAT format - it is actually NTFS, or so it claims.
Paragon's NTFS for Mac support page says the problem is usually due to third party drivers, not genuine Microsoft NTFS drivers. They recommend uninstalling Paragon's software, deleting all the NTFS drivers (without really saying how to do it, as far as I can see) and then reinstalling NTFS for Mac. Sounds like a lot of work to me.
I am going through the directories, and either creating new folders, or copying the old folders to the new SSD drive, which I formatted - the Get Info window says it is "Mac OS Extended (Journaled)".
So far I've managed to copy 9.99 GB, so I am not really expecting to go through a lot of steps to get the rest of the files transferred. The original Seagate HDD is only 1 TB, so I might be seeing the light at the end of the tunnel. AND, sometimes The entire folder and its contents copy and paste without the error 50 showing up.
That said, I have other HDDs that it would be nice to have backed up before they crash. Most are 4 or 5 TB. So I am grateful for any advice. And I am putting most of my data on iDrive, and also on iCloud, Backblaze, and DropBox, depending on what type of data it is. (I do have a Windows 11 Home OS laptop, which I don't use as much, but there are certain programs I use that haven't been ported to MacOS.)
