Button Start New Activity cannot start?

Question

i have created apps in eclipse with target sdk in API 15 and. I want to make button start new activity. i have created that code but i have a problem. when i run in on my phone ninetology stealh 2, when i click a button and my app has crash and my phone show me this :

"Unfortunately start"

i have tested it in others phone two and it show same problem. i also use more technique that i learn from thenewboston, vongella an other but still have same problem. here is my .xml and java code :-

menu.java

package com.mytuturkiu.mytuturkiu;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;                                                                                                                                                                                                                       
import android.widget.Button;
import android.content.Intent;

    public class Menu extends Activity {

      Button btnmodul;

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

          btnmodul = (Button)findViewById(R.id.btnmodul);      
            btnmodul.setOnClickListener(new View.OnClickListener() {

              @Override
              public void onClick(View v) {
          // TODO Auto-generated method stub
              Intent vokal = new Intent(v.getContext(),Modul_Vokal.class);
              startActivity(vokal);
          }
      } );

  }



}

Modul_vokal.java

package com.mytuturkiu.mytuturkiu;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;

public class Modul_Vokal extends Activity {

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

  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      // Inflate the menu; this adds items to the action bar if it is present.
      getMenuInflater().inflate(R.menu.modul__vokal, menu);
      return true;
  }

}

AndroidManifest.xml

<uses-sdk
    android:minSdkVersion="14"
    android:targetSdkVersion="15" />

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.mytuturkiu.mytuturkiu.Menu"
        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="com.mytuturkiu.mytuturkiu.Modul_Vokal"
        android:label="@string/title_activity_modul__vokal" >
    </activity>

</application>

what problem with my apps?..