To be honest, i'm kind of mystified why you'd need an onload
event to be triggered once attachMovie is complete, its
instantaneous. Unless of course you're mistaken attachMovie for
loadMovie, or you're using an exceptionally large movieclip from
the library or shared library.
Just having s second look you seem to be using a component
which aside from being the devils work, can take a while to
initialise before you can call methods on it like your