better way is just to shutdown server and boot it in gm only mode. noob players could just login and start shouting 'wtf is happening at this bugland' (worst scenario). mine verdict: useless.
This is Freya server. You need Freya client and system folder with correct client protocol version in order to connect.
Suggestion: search for systems, try other Freya server systems and try to login to your server. Do not forget to look at IP and ports configuration.