Personally I think the others might be jumping the gun a bit here.
A simple reason for getting that message and also not being able to find the virus is that it's simply a mIRC script with an on JOIN event that's causing the trouble. If that's what it is then simply typing /!remote off is a temporary solution until you can find precisely what script file is causing the problem. If you know any scripters I'd recommend having them take a look at your remote files, or if you know scripting take a look yourelf. Otherwise I'd recommend deleting your script files. Don't forget to turn your remotes back on again once you're sure the script is fixed/removed (/!remote on).
Obviously it's possible that it IS really a virus/trojan. But the chances are any good virus scanner would have detected it.
