admob getting an ad response. ErrorCode: 0 Failed to load ad:0

I have followed many answers about that error here, but my problem is not solved. Every time I run my app no ads appear and I get this error message in Logcat:

"There was a problem getting an ad response. ErrorCode: 0 Failed to load ad:0"

Here is my java code. What did I miss?

private void LoadAds() {


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


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


mAdView.loadAd(adRequest);

and here my xml layout with admob at the last lines

<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>

I cannot figure what the problem is. I'm new in android development.