I use the ad control with physics helper in a couple of apps, "Free Drop" and "Paint to Life." For both of those, I place the ad control inside a parent canvas on top of the game canvas (the one with the PhysicsControllerBehavior).
I would try subscribing to the AdControlError event and see wha the control reports... Here is my code -
= new AdControl("xx",
ads.Width = 480;
ads.Height = 80;
ads.AdControlError += new
void ads_AdControlError(object sender,
string err = e.ErrorDescription;