After doing a successful FM Server 16 install (upgrade from 15), the only remaining thing to do seemed to be to add the SSL certificates from the previous version. I added these manually, and then proceeded to stopping and starting the server. But the startup didn't seem to work. It seemed to be hanging.
I restarted the system and then proceeded to start over by first uninstalling FM Server 16. I also cleared the Java cache and the browser cache, as outlined in fms16_install.pdf.
I updated my Java, cleared its cache again, and restarted the system multiple times. But nothing seems to be working. I'm still getting the same error.