Numeric responses are sent by the server. mIRC has no control over what it receives.

Also, according to RFC1459 numeric 482 is as follows:
Quote:
482 ERR_CHANOPRIVSNEEDED
"<channel> :You're not channel operator"

- Any command requiring 'chanop' privileges (such as
MODE messages) must return this error if the client
making the attempt is not a chanop on the specified
channel.



Your network may be doing something strange.