Array actions error

CLIP1, CLIP2, CLIP3 AND CLIP4 BE THE INSTANCE NAME FROM 4 DIFFERENT MOVIE CLIPS… THE CODE BELLOW NOT WORK … ANY SUJESTIONS ?

[AS]
var clipAr:Array = [“clip1”,“clip2”,“clip3”,“clip4”];
for(q=0;q<clipAr.length;q++) {
var rAl:Number = Math.floor(Math.random() * (100 - 70)) + 70;
clipAr[q]._alpha = 0;
clipAr[q].alphaTo(rAl,1);
clipAr[q].onRollOver = cOver;
clipAr[q].onRollOut = cOut;
}
function cOver() {
this.tween("_y", this._y + 10, .5);
}

function cOut() {
this.tween("_y", this._y - 10, .5);
}
[/AS]