Bug on server

Hi,when I go on server, i have very lag,and i see everybody don't moves,and after i crash with this message : i.o.netty etc. after this i can't remember.Today i have the same bug but it's write: "disconnected from server". I think it's because i change my internet operator.Sorry for my bad english. It's on 1.7.4 but i can't write this.