D-Bus issues
The issue
D-Bus is how the Supervisor does most of the communication with the host, without this, multiple things that the Supervisor needs to do will fail.
The solution
If the D-Bus daemon is not running, start it.
If that does not help, reboot your operating system.
As a last resort, you need to reinstall the host running the Supervisor with one of the supported operating systems, see instructions here.