Android AdMob未显示在真实设备上

Question

AdMob在Android版本2.3和4.2的模拟器上正确显示，但在真实设备（Android版本4.0.4）上没有显示。错误是

12-22 19:35:56.930: ERROR/Ads(6311): JS: Uncaught ReferenceError: AFMA_getSdkConstants is not defined (http://media.admob.com/:1)
12-22 19:35:56.930: ERROR/Web Console(6311): Uncaught ReferenceError: AFMA_getSdkConstants is not defined at http://media.admob.com/:1

代码是

admob_preference.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
              android:layout_width="fill_parent"
              android:layout_height="fill_parent"
              android:gravity="center">
    <com.google.ads.AdView
            android:id="@+id/ad"
            ads:adSize="BANNER"
            android:layout_width="320dp"
            android:layout_height="wrap_content"
            ads:adUnitId="a150d2d17822fc0"
            ads:loadAdOnCreate="true"/>
</LinearLayout>

AdmobPreference.java

public class AdmobPreference extends Preference
{

    public AdmobPreference(Context context) {
        super(context, null);
    }

    public AdmobPreference(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    protected View onCreateView(ViewGroup parent) {
        //override here to return the admob ad instead of a regular preference display
        LayoutInflater inflater = (LayoutInflater) getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        return inflater.inflate(R.layout.admob_preference, null);
    }

}

的preferences.xml

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
    <com.nbrk.rates.AdmobPreference android:key="ad" />
</PreferenceScreen>