I doubt that's anything to do with mIRC directly, despite it specifying mirc.exe - I'm using v6.11 too on Win XP Pro SP1...and I've never had any problems thus far.
Perhaps other programs are conflicting with it? Have you tried running mIRC on it's own without other programs running?
And does this happen as soon as you start mIRC up, or after mIRC has been running for awhile..or is it just completely random? You may also like to run a virus scan just to be safe, I used to have Illegal Operations occuring with my mIRC a couple of years ago and I actually had a virus.
Perhaps someone will, hopefully, understand all that Windows jargon :P
Good luck.
Regards,
