ti.admob can show ads in emulator but cant in real devices.

http://developer.appcelerator.com/blog/2011/09/admob-for-android-module-tutorial-and-code.html

i follow this post to add ti.admob to my app. along with the following changes:

1. download the latest google admob sdk, put it to the modules/android/ti.admob/1.0/lib/, then delete the older one ti.admov v1.0 have.

2. change the configChanges in modules/andorid/ti.admob/1.0/timodule.xml to : android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|uiMode|screenSize|smallestScreenSize"

3. add <tool-api-level>14</tool-api-level> under <android xmlns:android="http://schemas.android.com/apk/res/android"> in the tiapp.xml and <modules><module version="1.0">ti.admob</module></modules>

4. copy the example from ti.admob module to my own app.js, put my own pubisher id;

after the 4 steps,it can load ads in the emulator(mobile sdk 1.7.5+goolge apis2.2/2.3+hvga), but when i try run in devices(samsung galaxy ace s5830, android 2.3), it cant load any ads, any ideas?

thanks in advantage;