No, it was a Plex goof. I've got past the Silverlight error message now. However, now when Netflix loads up in Plex, there are two buttons -- one for Preferences, where you sign into your account, and a second Netflix logo button that says "Sign up for free trial." That button is still there after one logs in (and after restarting Plex and restarting the PB). When you hit the button, it gives an error message: "Plex is having trouble communicating with [your PC]: There was an internal server error while trying to respond to the client request please check the server logs for more details." You have the option of responding to this error message with "Ignore" or "Pick A New Server." Ignore just brings you back to the two button screen. I can't beyond that. Thanks, Plex!
Also, as I mentioned, a fair number of the movies on my PC simply won't play, and there's no rhyme or reason that I've been able to find to distinguish between those that will play and those that won't (generally, all of my movies are mp4 files). When I tap on one of the movies that won't play, I get the (fatal) error message "Oops! Plex ran into a problem -- please hold on a second while we recover." And then the thing crashes and I'm back to the PB home screen. Thanks, Plex!
OK, now there is some potentially very helpful advice. I emphasize "potentially," however, for how does run Plex Media Server in compatibility mode? It's not a standalone program -- it uses the web browser. So are you saying I have to run my web browser in compatibility mode??? That's convenient. Also, it's not like Windows 8 just appeared yesterday. I've been running it for the better part of last year. You'd think a developer would make the effort. Thanks, Plex!