If you get this is means that that you haven’t installed the database application on your PC/Mac
OR
It means that the extension can’t connect to it. It happens when you install the extension first and then the database app. Since the installer kills any running Java application (and a small part of extension – the part that communicates from the extension to the app – is in Java) you need to RESTART THE EXTENSION. You can do this by going to extensions and just flip the extension’s on/off switch (or using the reload button – which basically does the same).