Might not be your case, but the lag has been very bad for me when connecting. Luckily I can connect. Survival server is only 1.7 —sorry if you already know that.
I've experienced something similar to the past with my building server. I just restarted the server and the error stopped. But, MCSG is not my server, lol.
What I can recommend you is delete the servers.dat file in your minecraft folder —will delete all the servers you added— and see if it works. If not, make a clean install of Minecraft. Make sure to remove the .minecraft folder if you're doing a clean install.
Also, it could be the MS you're getting to the server. If its too bad, you could possibly not be able to connect to the server.