So - if you see this error dialogue when starting the admin part of EpiServer; you most likely are not having your webserver configured correctly (as the error suggest ;-)). To reflect updates to the database - the system is using websockets to communicate that to the webclient rendering the administration website.
Therefore - this is due to a missing WebSocket configuration/installation on the webserver (IIS). To remedy this open Programs and Features on Windows (Server or Client) and add WebSocket as seen below.
That is what it takes.