I don't know if it's a coincidence but, the server goes down when I log in. I was digging down and it crashed yesterday. This morning the dynmap was loading so I thought it might be back up, so I logged in and immediately after the server closed again.

Error message :

Connection Lost
Internal Exception: java.io.IOException: An existing connection was forcibly closed by the remote host

Then the dynmap goes down : 503 Service Unavailable.