Need help with Tween class... can't tween alpha

programming flash
1 

var picStartAlpha1_out:Number = pic1_out.alpha;
var picEndAlpha1_out:Number = 0;
var picAlphaDuration1_out:Number = 700;

var picTweenAlpha1_out:Tween = new Tween (pic1_out,"alpha",Regular.easeInOut,picStartAlpha1_out,picEndAlpha1_out,picAlphaDuration1_out,false);

I can get the picture to fade in with the same code, by replacing _out with _in. But now it won’t fade out. Any suggestions or ideas?