Android : How to use Admob phonegap plugin with ios and android 2014

I am using https://github.com/gooogleadmob/admob-phonegap admob phonegap plugin this is my step

cordova create demo com.admob.demo demo cordova plugin add c:\admob-phonegap cordova platform add ios cordova platform add android cordova run ios

sometimes this work well ,but sometimes it show error cannot fount plugin com.admob.AdmobPlugin,check if that is defined

how to use admob phonegap plugin ,is there any error I do?