Google admob errod on return ad
<p>I keep getting this error in my debug when ads are about to be displayed.</p>

<pre><code>07-16 14:35:29.630: INFO/Ads(12137): onFailedToReceiveAd(Ad request successful, but no ad returned due to lack of ad inventory.)
</code></pre>

<p>What does this mean and how do i fix it?</p>
