Dynamic Referencing

Hi, I’m having some trouble trying to dynamically reference a nested movieClip, like this:

// – start –
for (i = 0; i < 2; i++) {
_root[“main”+“MC”]._x += 2; // This works fine.
_root.mainMC[“nestedMC”+i].x += 2; // This fails horribly. ;;
}
// – end –

Any ideas?