Can't send a message in multiplayer without crashing the game...

Put the summary of the bug you're having here

What I expected to happen was...:
I typed a message, so everybody can read it.

What actually happened was...:
Upon pressing Enter to send the message, the gamed brutally crashed. It happens all the time.

Steps to Reproduce:
NB: Other people can send messages,they have no problem.
Go on a multiplayer server. (the ones I go to seem to work with Bukkit due to the mods they have)
Type a message.
Send it.
Rage because the game crashed.