Sometimes, Roon gets confused about the identity of the connected server and thinks the server that it can see is not the one that it is currently connected to.
Have you tried selecting ‘Select a different Roon Server’?
This should present you with a selection of all of the available servers (which is typically just one) from which you select the one you want to log onto.
Once you gone through the login procedure you may then be presented with a screen saying that you have logged on to a different server. This screen will also present an ‘Unauthorize’ button. Selecting that will allow the connection to your server to procede.
@Wade_Oram is correct in their comment above - I also wanted to add that, based on your screenshot, it doesn’t look like Roon Server is running (you can typically see the Roon jellyfish in the upper right-hand taskbar.) Here’s a quick video on how to start Roon Server: