For example, if you show AdSense or other competitive contextual ads on your site at the same time as a YPN ad, then you could get banned. "It's okay to rotate these ads along with Yahoo ads as long as they don't appear at the same time," says Marc Gibson.
Also, if you have an international Web site, make sure to exclude pages in languages other than English or Spanish from your YPN roster, as the contextual ads are only supported in those two languages at this time. And don't try to pump your pages full of YPN ads. The system only allows three ad units per page.