Screen experts: gotoNextSlide() help needed

I want a slide show built with Screens to play automatically. Some screens have timeline animations in them some don't.
For convenience, the slides are arranged in the following hierarchy:

Presentation (Master slide - no content)

Container slide 1 (To group all slides under same topic - no content)
Content slide 1 - with timeline
Content slide 2 - with timeline
Content slide 3
Content slide 4
Container slide 2 (To group all slides under same topic - no content)
Content slide 1 - with timeline
Content slide 2
Container slide 3 (To group all slides under same topic - no content)
Content slide 1 - with timeline
Content slide 2
Content slide 3
Etc...

There are two Behaviors attached to the master slide for transitions: on (hideChild) and on (revealChild). And autoKeyNav is set to False for each container slide and to Inherit for content slides.

I use the code: (Taken from another thread in this forum. )

stop();
function goNext(){

_parent.currentSlide.gotoNextSlide();
clearInterval(timer);
}
var timer = setInterval(goNext, 4000);

I put it on the last frame of slides that have a timeline and on the unique frame of slides that don't have a timeline.
It works until the first slide without a timeline and stops. (Content slide 3 in my example.)

If I enable the autoKeyNav property, the arrow keys do work fine.

The above code seems to work only on slides with timelines.
How or where should I put the code on slides that have no timeline?

Can any guru help?
THNX.