android app showing error (unfortunately,Sudoku has stopped)

hello i am learning android from book hello,android and i am stuck in chapter 3 . I am trying to show a new activity containing information about Sudoku game when user click the about button but dwe to a some reason when i ran the app it shows me unfortunately,Sudoku has stopped.I tried to solve by myself but unable to figure out the problem .I need your hellllllllllp

here the files are listed below

AndroidManifest.xml

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.android.sudoku.Sudoku"
        android:label="@string/app_name" >
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".About"
        android:label="@string/about_title">
    </activity>

</application>

about.xml

    <?xml version="1.0" encoding="utf-8"?>
<ScrollView
    xmlns:android="http://ift.tt/nIICcg"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="10dip"
    >

    <TextView
        android:id="@+id/about_content"
        android:layout_height="wrap_content"
        android:layout_width="wrap_content"
        android:text="@string/about_text"/>

</ScrollView>

activity_sudoku.xml(my main activity)

<LinearLayout xmlns:android="http://ift.tt/nIICcg"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:gravity="center"
android:orientation="vertical"
android:background="@color/background"
android:padding="30dip" >

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="25dip"
    android:text="@string/main_title"
    android:textSize="24.5sp" />

<Button
    android:id="@+id/continue_button"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="@string/continue_label" />

<Button
    android:id="@+id/meow"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/new_game_label" />

<Button
    android:id="@+id/about_button"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/about_label" />

<Button
    android:id="@+id/exit_button"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/exit_label" />

<Button
    android:id="@+id/ext_button"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="@string/dialog_label" />

</LinearLayout>

Sudoku.java

package com.android.sudoku;

//import android.support.v7.app.ActionBarActivity;
//import android.support.v7.app.ActionBar;
//import android.support.v4.app.Fragment;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.os.Bundle;
//import android.view.LayoutInflater;
//import android.view.Menu;
//import android.view.MenuItem;
import android.app.Activity;
//import android.view.View;
//import android.view.ViewGroup;
//import android.os.Build;

public class Sudoku extends Activity implements OnClickListener{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sudoku);

        // setup click listeners for all the button
        View continueButton = findViewById(R.id.continue_button);
        continueButton.setOnClickListener(this);

        View newButton = findViewById(R.id.new_button);
        newButton.setOnClickListener(this);
        System.out.print("here ");
        View aboutButton = findViewById(R.id.about_button);
        aboutButton.setOnClickListener(this);
        System.out.println("no error");
        View exitButton = findViewById(R.id.exit_button);
        exitButton.setOnClickListener(this);

        View dialogButton = findViewById(R.id.ext_button);
        dialogButton.setOnClickListener(this);

        if (savedInstanceState == null) {

        }
    }


    public void onClick(View v)  {

        switch(v.getId()) {

        case R.id.about_button:
            Intent i = new Intent(this,About.class);
            startActivity(i);
            break;
        // more buttons go here id any
        }

    }

}

About.java

package com.android.sudoku;
import android.app.Activity;
import android.os.Bundle;
public class About extends Activity {
protected void onCreate(Bundle savedInstanceState)  {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.about);
}
}