Same problem here. I did what you recommend but my ads dosen't rotate
I've set up zones and placements. I've placed 3 ads to run at random. Only one is showing up.
To rotate your three ads, you'll want to target them all to the same Placement. Set the Placement's Content Order field to "Random" and target the Placement to your Zone.
For additional info, see the ad-rotator recipes in the AdPlugg Cookbook here: