I followed the tutorial and put the admob code into a test app and everything seemed to work and I saw the test ads displayed on the screen. I'm not sure why test ads instead of real appeared on the screen, but the code seemed to be working. When I put the admob code into the real app, I no longer see the test ads. Logcat shows "failed: Ad request successful, but no ad returned due to lack of ad inventory", so I'm not getting any ads on the screen. I'm not sure what I did to disable the test ads, and I'm not sure how to bring them back. Any help would be appreciated.
"Lack of inventory" means that there are no ads to show.... try later.
Also, have you tried to add Google AdSense adds in your admob control panel ? It can help a little!