So far as I understood you, you can't write anything in the chat, but on the screen you wrote something in the chat, pls articulate you better.
But if it's that you can't write anything in the chat window, open in pack root.epk and replace uichat.py with another one you know you can write in the chat window.
Now pack it and done
If you mean something else pls define it so I could help you^^