Error "Message rejected for containing invalid UTF-8"

[niponic]

Hello, excellent work, I'm using it on bitchx but I can't use accents in words and some characters such as: "ç ã ê é á à í" and others more.
In the window it appears correctly, but when sending to the server I get the following error:
··· Odd server stuff: "FAIL PRIVMSG INVALID_UTF8 :Message rejected for containing invalid UTF-8"

Any way to resolve this? I tried with many servers