That bar has been seen by many people using Win7, which I assume you have if you're seeing that. I've seen it as well, but it's not always there and I don't know the actual cause. I think I remember a bug report about that a few months ago that Khaled responded to about trying to find the case, but I don't know if anything came of that. I'd try restarting mIRC and/or your computer to see if it goes away because, like I said, it's not always there on mine, but I've seen it now and then.
And how can you stand that color background? It can't be good for your eyes staring at that non-stop.
