This error appears any whenever the Create Plugin is not installed or when the plug in needs to be updated or needs permissions.
If you click in the
Help button, it will show some usual fixes.
First of all, please check if the plugin is running. You should see the icon in the taskbar and its colour should be blue/green. If you don't see the icon, open the plugin by running Arduino Create Agent. If the icon is grey, click on it and then click on Open Plugin.
If this is happening in school computers, it might be related to the app rights, please consult with the IT department to allow/install the Arduino Create Chrome app on all the devices. You may share the instructions available on this tutorial.