duplication level

[Overfiend]

Hi everyone,
ok im having some trouble with a movie that im making.Ok i have a global variable called"N" set to 70.
i have a movie clip on the main stage called "Ninja" and on this ninja movie clip i have the following code:

code:

---

 onClipEvent (enterFrame) {

	if(this.hitTest(_root["mc"+90])){

		this.gotoAndStop(75);

		_root["mc"+90].gotoAndStop(21);

		if (N>=70 && N<=89) {	

		duplicateMovieClip(_root.Ninja, "NMC"+N, N);

		N++;

	}else {N = 70;}

}

}

---

so i want every time the movie clip is hit to duplicate its self between the levels 70 - 89 so there will never be more than 19 instances on screen. i know the hit part works because it is sending the ninja movie to frame 75 as stated. However it is duplicating the movie always to layer 70 and not incrementing thus deleting the original movie on layer 70 so there is only one instance appearing at a time.

also when debugging i get the following results:
Movie Clip: Frame=10 Target="_level0.NMC70.instance33"
Movie Clip: Frame=10 Target="_level0.NMC70.instance34"
so its copying the instance but not assigning a new level

any help would be absolutly great as i havent got much hair left on my poor balding head.

P.S. using MX