What type of hosting did you sign up for? Ad-free or ad-enhanced? Advanced packages require a text link ad, while corporate packages require a banner ad. I believe you have either 3 days or a week to get the ads up, I can't recall which it is.
What package did you sign up for? The only plan that doesn't require ads is the static plan. All others(advanced and corporate) require their proper ads to be placed on all publicly viewable pages.