can't sign in with Plex Media Server app



OS X 10.11.6, PMS
can't access Plex through the Plex Media Server app on my desktop all of a sudden; nothing has changed, as far as I know, but now I get "There was an error signing in". However, if I go to the website and sign in there I can access my Plex media and also with Plex Media Player on my laptop.

What's going on here? It's kind of inconvenient not being able top click on 'Open Plex...' in my menu bar to gain access. Any suggestions?