your clear response was given to you in your first reply. the main cause of random break errors is due to the ctrl-break or ctrl-pause key getting stuck. You have to press them a few times. I've solved this issue myself with this method in the past, and I've never been unable to solve it using this method, nor have I ever seen this happen unintentionally without the stuck keys being the cause, so I'd bet this is your problem too.
If that doesn't work, reinstall mIRC, as suggested.
