Thanks for the information, Michael.
This seems a bit confused, on Microsoft's side, however. The System Image Backup feature has been working fine through build 1803 and the UI still shows it in 1809, it just happens to fail with an unexpected error. If the error was "feature has been removed" that would be one thing, but it is not saying that ... the error claims that the drive is write-protected, which it is not.
The Wikipedia article on Windows' Backup and Restore (https://en.wikipedia.org/wiki/Backup\_and\_Restore) says that Backup was deprecated in Windows 8, removed in Windows 8.1 and then restored in Windows 10.
I also found this article -- https://support.microsoft.com/en-us/help/4034825/features-that-are-removed-or-deprecated-in-windows-10-fall-creators-up -- which states that System Image Backup is deprecated, but the UI in control panel gives no indication of this.
I may look into Macrium based on what you have said, but it seems to me that this is not a case of a feature being deprecated ... it seems to be simply a bug.
I do use File History, but that will not help me much if my primary hard drive dies. I have used Windows Backup to do a whole drive restore in the past and it was a life-saver. If they do remove this feature, I will miss it.