In Minecraft, on servers, if i try to chat, my Minecraft shutsdown.

I was on a PVP server, and was asked to team with someone.I typed sure, and I expected it to be sent for the other players to see.But insted, my Minecraft completely shutdown.I logged back on, and tryed again to chat.It shutdown again... . 1. Log on to a server. .2 Try to chat .3 It shutsdown . Thank you for your time