按钮点击admob异常

Question

点击后退按钮（手机后退按钮）点击播放声音按钮我的应用程序崩溃了，当我点击admob adverseting时，我有一个播放声音的按钮 我的例外日志是：

06-15 00:58:17.774: W/dalvikvm(17141): threadid=1: thread exiting with uncaught exception (group=0x40a751f8)
06-15 00:58:17.782: E/AndroidRuntime(17141): FATAL EXCEPTION: main
06-15 00:58:17.782: E/AndroidRuntime(17141): java.lang.IllegalStateException
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.media.MediaPlayer.isPlaying(Native Method)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at com.alcsoft.yasiniserif.MainActivity$3.onClick(MainActivity.java:113)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.view.View.performClick(View.java:3519)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.view.View$PerformClick.run(View.java:14140)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.os.Handler.handleCallback(Handler.java:605)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.os.Looper.loop(Looper.java:137)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at android.app.ActivityThread.main(ActivityThread.java:4424)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at java.lang.reflect.Method.invokeNative(Native Method)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at java.lang.reflect.Method.invoke(Method.java:511)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
06-15 00:58:17.782: E/AndroidRuntime(17141):    at dalvik.system.NativeStart.main(Native Method)