Why does the minecraft server crash when I join?

I used to play on this server 24/7 but then I went to the nether and used the command /world to get out instead of the portal. I was on with a few friends and then it just crashed! I came on 1 day later and nothing is different. Now when I join on that account it just crashes the server. When I join with my alternate account it is regular nothing different. Please help! PS. It crashes the server not my client.

Someone is probably just kicking you out. People do that