rare multiplayer server loggin bug

failed to login: java.io.IOException: server returned HTTP response 503 for URL:
http://session.minecraft.net/game/joinserver.jsp?user=dck1234&sessionId=token%3A8f86d86bed21442791f4e9d627759901%3A7e83e09fbec94a77a4f6778aa5ccd7fd&serverId=-3b2f79abd291ec777adaa4bc1bbab8e8851b4b64

this is what i got if i wana login in a minecraft server, i don't know what it is.
1.7.2 don't have the bug, only 1.6.4 servers