ActionScript 2.0 :: Checking To See If A Mc Container Is Empty

I'm working with a window scroller component, where the dynamically loaded scrolling content has buttons that load attach mc's to a clip holder in front of the window scroller. To do this I use this bit of code, which works fine:

Code:
calendarPagesBtn_mc.onRelease = function(){
_level0.slideHolder_mc.attachMovie("calendarPages", "calendarPages", _level0.slideHolder_mc.getNextHighestDepth());
this.enabled = false;
};

The "this.enabled=false" is to deactivate the button in the scroll content, otherwise it will still be active in the background. So far so good.

What I need to do, once the "close" button on the attached mc is clicked, is re-enable the button. I'm thinking the way is to check if the attached mc has been unloaded, which I'm trying to do with this:

Code:
if (!_level0.slideHolder_mc.content)
this.calendarPagesBtn_mc.enabled = true;