I am trying to add ads to my app but I don't know how I followed the instructions from this site: https://developer.android.com/google/play-services/ads.html I did step 1 and 2 in the getting started column, I imported the google-play-services_libs to my workspace then I referenced it in my app and I added this code in my mainfest: <meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" /> I opened the sample ad and copied this code to my 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/res-auto" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@android:color/black" android:gravity="center" android:orientation="vertical" > <com.google.android.gms.ads.AdView android:id="@+id/adView" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_alignParentBottom="true" android:layout_alignParentLeft="true" ads:adUnitId="@string/ad_unit_id"/> but I am getting this error: The following classes could not be instantiated: - com.google.android.gms.ads.AdView so do you know how to fix this problem and can you tell me what should i write in the java to make in work thanks