Segui muitas respostas sobre esse erro aqui, mas meu problema não foi resolvido. Toda vez que executo meu aplicativo, nenhum anúncio é exibido e recebo esta mensagem de erro no Logcat:

"Ocorreu um problema ao obter uma resposta do anúncio. ErrorCode: 0 Falha ao carregar o anúncio: 0"

Aqui está o meu código java. Do que eu senti falta?

private void LoadAds() {

 AdView mAdView = (AdView) findViewById(R.id.linearLayoutAdmob);

 AdRequest adRequest = new AdRequest.Builder().build();

 mAdView.loadAd(adRequest);

e aqui meu layout xml com admob nas últimas linhas

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:ads="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 android:orientation="vertical"
 android:background="@drawable/background_play"
 tools:context=".MainActivity" >

<RelativeLayout
    android:id="@+id/rlayout1"
    android:layout_width="fill_parent"
    android:layout_height="0px" 
    android:padding="5dip"       
    android:layout_weight="2.3" >

    <com.aapps.find.TouchImage
        android:id="@+id/gameimage1"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:scaleType="fitXY"
        android:src="@drawable/ic_launcher" />

    <ImageView
        android:id="@+id/hitimage1"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@drawable/hit"
        android:visibility="invisible" />

    <ImageView
        android:id="@+id/errorimage1"
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:src="@drawable/miss1"
        android:visibility="invisible" />
</RelativeLayout>
<RelativeLayout
    android:id="@+id/rlayoutprogress"
    android:layout_width="fill_parent"
    android:layout_height="0px"
    android:layout_weight="0.1" >
   <com.aapps.find.utility.SaundProgressBar
    android:id="@+id/progressBar"
    style="@style/Widget.ProgressBar.RegularProgressBar"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"/>
   </RelativeLayout>
   <RelativeLayout
    android:id="@+id/rlayout2"
    android:padding="5dip"  
    android:layout_width="fill_parent"
    android:layout_height="0px"
    android:layout_weight="2.3" >
   <com.aapps.find.TouchImage
        android:id="@+id/gameimage2"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:scaleType="fitXY"
        android:src="@drawable/ic_launcher" />

    <ImageView
        android:id="@+id/hitimage2"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@drawable/hit"
        android:visibility="invisible" />

    <ImageView
        android:id="@+id/errorimage2"
        android:layout_width="30dp"
        android:layout_height="30dp"
        android:src="@drawable/miss1"
        android:visibility="invisible" />
</RelativeLayout>
<RelativeLayout
    android:id="@+id/rlstatus"
    android:layout_width="fill_parent"
    android:layout_height="0px"
    android:layout_weight="0.3" >
    <TextView
        android:id="@+id/scoreCount"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginLeft="15dp"
        android:textSize="16sp"
        android:textStyle="bold"
        android:textColor="#fffd7a"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:layout_alignParentLeft="true"/>

    <TextView
        android:id="@+id/hitCount"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:textSize="16sp"
        android:textStyle="bold"
        android:textColor="#fffd7a"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:layout_marginLeft="15dp"
        android:layout_toRightOf="@id/scoreCount"/>

    <ImageView
        android:id="@+id/imgSound"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_alignParentRight="true"
        android:layout_marginRight="15dp"
        android:src="@drawable/sound" />
    <ImageView
        android:id="@+id/imgHint"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginRight="15dp"
        android:layout_toLeftOf="@id/imgSound"
        android:src="@drawable/hint" />
    <TextView
        android:id="@+id/hintCount"
        android:layout_width="wrap_content"
        android:layout_height="fill_parent"
        android:layout_marginRight="26dp"
        android:textSize="16sp"
        android:textStyle="bold"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:layout_toLeftOf="@id/imgSound"/>
</RelativeLayout>


      <com.google.android.gms.ads.AdView
    android:id="@+id/linearLayoutAdmob"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_centerHorizontal="true"
    android:layout_alignParentBottom="true"
    ads:adSize="BANNER"
    ads:adUnitId="@string/admob_id">
</com.google.android.gms.ads.AdView>
</LinearLayout>

Não consigo descobrir qual é o problema. Eu sou novo no desenvolvimento android.