Select Automatisk registrering af instillnger by clicking that box.
Press ok and restart the browser, go onto the FH site, press ctrl + f5.
If you still have issues go into "Advanced" and try to reset your browser settings to default so no settings are still active.
That message only appears if the client is going through a proxy to connect to this site, we do not allow that since some random "waste" try to use this to cause havoc on the site or just be drama llamas.