This is nothing to worry about.
Most of the time, all it means is the the dns server didn't receive a reply in a timely manner when it sent the request for your hostname. This can (and in my opinion probably is) simply a matter of lag between two different networks.
In my experience this does not affect your ability to connect to a network, chat on channels, use query/pm windows, or anything else that you normally use mIRC for.
