I can usually track down most errors when doing an import.
However, has anyone moving a course from Bb to Canvas get a "Failed" message along with "An unexpected error occurred"?
After I posted this question, I think I have the answer.
I increased the "File storage" in "Settings" - "Course Details" and the error went away.
So now I know what that an "unexpected error" can be fixed by changing the File Storage amount.