Problem setting Propperties

hi, i attached a movie Clip inside the clip “container” and stored the return reference in “obj” to set parameters afterwards. it works for ._x and ._y and ._rotatoion, but not for ._xscale and ._yscale.
the attached movie has a motion tween inside.
this is the code i use:

			obj=container.attachMovie("spray","spray"+c,c);
			obj._xscale=5;
			obj._yscale=5;
			obj._x=this._x + xdist*this._z;
			obj._y=-(this._y + ydist*this._z);
			obj._rotation=-(360*this._anglez)/(2*Math.PI);

what could be the problem?
thanks