Thanks, that's helpful. I've got the Units stuff working OK now, but I was playing around with sounds (Play, EmitSound, etc.) and had to quit and restart MMA before it would actually make noise. At one point in the process, just as with Units, it appeared that something was being loaded from the Wolfram site. On the other hand, the few Entity things that I've tried from the Help examples (e.g., Entity["Mythology"]["Properties"]) have worked OK.
How do you reset Paclet data? Via PacletUpdate, or ...?