so i have an MC with an elastic move script which works fine- however when i try to apply the script to another MC in the same time line it fails

the action call is :
Movieclip.prototype.elasticMove = function(target, accel, convert) {
step = step * accel + (target - this._x) * convert;
this._x += step;
}

the event handler on the MC is this:

onClipEvent (enterFrame) {
elasticMove(_root.newX, 0.6, 0.6);
}
onClipEvent (load) {
_root.newX = 200;

}

i have tried renaming the function and the call, say to "elasticMove2" for the other MC but that doesnt work.
i have tried some simple tests anfd found that you simply cant use the call with two seperate mc's

anyone have any insight as to why this is or a workaround?