Me guess: You have property tried to show a ad before the ads even have been init (which sometimes can take a while). this can happens if you launch a ads too early, etc on launch.
This why im actuelly diddent show a ad in startup in Genius Greedy Mouse, but first do that much later when you leave a level.
Howover, just add a nullpointercheck to avoid it in public void show(int status), and then its fixed. etc mInterstitialAd object does first create after a init has been done.... which is done asyncon.
PS. Fixed in next release. its does now first try to show the ads after the init have been property done and a load has been loaded. If a ads has newer been loaded, then its will fails gracefull with no ads to been show (and you can checkout its status).