Session bus usage to talk to systemd fails on Ubuntu

Here is error details

MethodError(OwnedErrorName(ErrorName(Str(Owned("org.freedesktop.DBus.Error.Spawn.ChildExited")))), Some("Process org.freedesktop.systemd1 exited with status 1"), Msg { type: Error, sender: UniqueName(Str(Borrowed("org.freedesktop.DBus"))), reply-serial: 2, body: Signature: [
        s (115),
] })

same method working for blocking proxy though, need help ...