Admob policies in android applications

i just want to integrate AdMob in my application and have the following XML:

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4"
    xmlns:ads="http://ift.tt/GEGVYd"
    android:id="@+id/container"
    android:layout_width="fill_parent"
    android:layout_height="match_parent"
    android:background="@drawable/background"
    android:orientation="vertical"
    tools:context="MainApp"
    tools:ignore="MergeRootFrame" >

    <TextView
        android:id="@+id/mainHeaderTextView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:paddingBottom="15dp"
        android:paddingTop="15dp"
        android:scaleType="center"
        android:text="@string/app_name"
        android:textSize="25sp" />



     <ListView
            android:id="@+id/mainListView"
            android:layout_width="fill_parent"
        android:layout_height="0dp"
        android:layout_weight="1"
        android:paddingBottom="25dp"
        android:paddingLeft="10dp"
        android:paddingRight="10dp" >
    </ListView>

    <com.google.android.gms.ads.AdView
        android:id="@+id/adView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        ads:adSize="BANNER"
        ads:adUnitId="my_unit_id" >
    </com.google.android.gms.ads.AdView>

</LinearLayout>

The Java Code is as follows:

AdView adView = (AdView) this.findViewById(R.id.adView);
        AdRequest adRequest = new AdRequest.Builder().build();
        adView.loadAd(adRequest);

When i am starting the app, i get error messages like "The page at about about: blank displayed insecure content from gmsg://....."

I read about the google policies here.

I think my problem is described at the last part "Ad covering app content (Not recommended - against policy)". But how to solve this? Any ideas?

UPDATE: After installing the app on a real device, i get ads. What is the reason for this behaviour?