Everything works! Hurrah!
Thanks again, tremendously, for all your help, Danny. You're a champ.
I had done all that, but possibly not in the correct order. I followed most of the suggested path at the bottom of d=4533, and that seems to have fixed it up. Possible that I was running into the same issue: reinstalling Rserve, which 'mostly worked', but hadn't killed the running process first. So when I then restarted it, it was muntered.