I haven't posted here lately because Typepad, which hosts this blog, suddenly started rejected my login when I used my editor, MarsEdit, to post new articles. In fact, after some excellent tech support from the MarsEdit creator, I discovered that Typepad was rejecting all XML-RPC login attempts for my ID.
I reported this to Typepad tech support about June 23rd. Today, July 4, I finally got a workaround. I'm posting it here in case another Typepad user finds they can't login and wants a more speedy response.
The answer is that there is "something wrong" with my user ID on Typepad. They're looking into it, but until it is resolved I can log in with my account's registered email address. That does work, and this alternative form of username is not documented or I would have tried it several days ago.