It looks like some sort of ban from the network. This has nothing to do with mIRC itself, it is network specific. Check
this thread for information.
You may also want to check out (and post on)
GameSurge's Forums and see if it's a common issue (use their search feature) or post a new thread and see if someone can help you.
It doesn't look like an error that has anything to do with mIRIC however, so there's not much we can do. Your best bet is to talk to the network administration.
G'luck!
Regards,