SonarLint cannot connect to SonarQube Server

The plugin the message is referring to is the Sonar Java Plugin. Log in to Sonar as admin, go to Administration/System/Update Center and you'll see that the current installed plugin version is 3.0. Update it to the newest version available and it should work.

[Edit] - The upgrade is triggered by just clicking the button, but after it is downloaded and installed, you'll have to restart the Sonar server.