Unable to find explicit activity class Android Eclipse error

MediaPlayer mp  = MediaPlayer.create(getApplicationContext(), R.raw.mymp3file);
mp.setLooping(true);
mp.start();

float f = 0.f;
boolean bIsNaN = Float.isNaN(f);
boolean bIsInfinite = Float.isInfinite(f);

 double d = Math.sqrt(-10);
 boolean b = Double.isNaN(d);

public class TimerActivity extends Activity {
TextView hTextView;
Button hButton, hButtonStop;
private Handler mHandler = new Handler();
private int nCounter = 0;
@Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        hTextView = (TextView)findViewById(R.id.idTextView);
        hButton = (Button)findViewById(R.id.idButton);
        hButton.setOnClickListener(mButtonStartListener);
        hButtonStop = (Button)findViewById(R.id.idButtonStop);
        hButtonStop.setOnClickListener(mButtonStopListener);
    } // end onCreate

View.OnClickListener mButtonStartListener = new OnClickListener() {
	public void onClick(View v) {
		try {
			mHandler.removeCallbacks(hMyTimeTask);
         //        Parameters
         //        r  The Runnable that will be executed. 
         //        delayMillis  The delay (in milliseconds) until the Runnable will be executed. 
                       mHandler.postDelayed(hMyTimeTask, 1000); // delay 1 second
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
};


private Runnable hMyTimeTask = new Runnable() {
	   public void run() {
		   nCounter++;
	    	   hTextView.setText("Hallo from thread counter: " + nCounter);
	   }
	}; 
/**
 * 
 */
    View.OnClickListener mButtonStopListener = new OnClickListener() {
    	public void onClick(View v) {
    		 mHandler.removeCallbacks(hMyTimeTask);
    		
    	}
    };
}

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="//schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
	android:id="@+id/idTextView"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="@string/hello"
    />
<Button android:text="Button" 
android:id="@+id/idButton" 
android:layout_width="wrap_content" 
android:layout_height="wrap_content"></Button>
 
 <Button android:layout_width="wrap_content" 
 android:layout_height="wrap_content" 
 android:id="@+id/idButtonStop" 
 android:text="Stop"></Button> 
    
    
</LinearLayout>

public class DictionaryProvider extends ContentProvider {
    String TAG = "DictionaryProvider";

//    public static String AUTHORITY = "com.example.android.searchabledict.DictionaryProvider";
// change to your new package name
public static String AUTHORITY = "com.myweb.mysubdomen.searchabledict.DictionaryProvider";
    public static final Uri CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/dictionary");


// in AndroidManifest.xml
//change com.example.android to your package e.g. com.myweb.mysubdomen
<!-- Provides search suggestions for words and their definitions. -->
        <provider android:name="com.example.android.searchabledict.DictionaryProvider"
            android:configChanges="keyboard|keyboardHidden|orientation"
                  android:authorities="com.example.android.searchabledict.DictionaryProvider" />

        <!-- Points to searchable activity so the whole app can invoke search. -->
        <meta-data android:name="android.app.default_searchable"
            android:configChanges="keyboard|keyboardHidden|orientation"
                   android:value=".SearchableDictionary" />

// I change like this:
        <!-- Provides search suggestions for words and their definitions. -->
        <provider android:name=".DictionaryProvider"
            android:configChanges="keyboard|keyboardHidden|orientation"
                  android:authorities="cz.okhelp.android.searchabledict.DictionaryProvider" />

        <!-- Points to searchable activity so the whole app can invoke search. -->
        <meta-data android:name="android.app.default_searchable"
            android:configChanges="keyboard|keyboardHidden|orientation"
                   android:value=".SearchableDictionary" />

<searchable xmlns:android="//schemas.android.com/apk/res/android"
        android:label="@string/search_label"
        android:hint="@string/search_hint"
        android:searchSettingsDescription="@string/settings_description"
        android:searchSuggestAuthority="cz.okhelp.android.searchabledict.DictionaryProvider"
        android:searchSuggestIntentAction="android.intent.action.VIEW"
        android:searchSuggestIntentData="content://cz.okhelp.android.searchabledict.DictionaryProvider/dictionary"
        android:searchSuggestSelection=" ?"
        android:searchSuggestThreshold="1"
        android:includeInGlobalSearch="true"
        >
 </searchable>