this seemed to do the trick, added some trace actions so you can see what is going on:

Code:
isPaused = true;
this.movieClip.play_btn.onRelease = function() {
	isPaused = !isPaused;
	trace ("Value of isPaused: " + isPaused);
	_root.movieClip.gotoAndStop(isPaused? 1 : 5);
	trace ("MovieClips Current Frame: " + _root.movieClip._currentFrame);
}
this line of code allows it to work:

Code:
_root.movieClip.gotoAndStop(isPaused? 1 : 5);
but this didn't:

Code:
this.movieClip.gotoAndStop(isPaused? 1 : 5);
the result was an undefiined object. you would have to write a new constructor function in order for this.movieClip.gotoAndStop(isPaused? 1 : 5) line of code to be applicable.