Please verify this:

this.aro_mc.aroinvisible.aroa_btn.onRelease = function() {
_root.gotoAndPlay("primera");
}
this.aro_mc.aroinvisible.arob_btn.onRelease = function() {
_root.gotoAndStop("segunda");
}
Why doesnt this control my main timeline?

Hi,

Syntax seems fine so only two other causes I can think... one, your reference
isn't correct for the button actions...

or,
you have loaded this to something other than _level0. Each _level# has it's
own independant _root timeline.

sorry if that isn't much help,
cheers,