in your *completely clean* mIRC, type
//echo -a $os $version $md5($mircexe,2) $script(0) $dll(0) $com(0) $isdde($ddename)
and report the results here.
Also, are you using any Winamp (or WMP) plugins to show your current playing song in mIRC or similar dlls that send messages to mIRC?
