Erro ao retornar consulta em listview

Pessoal,

Estou tentando passar as informações da tabela Contatos para um listview. Este listview está na tela principal da aplicação, então, assim que eu abrir a aplicação, os nomes dos contatos e o grupo ao qual eles pertencem devem aparecer, porém ocorre um erro e minha aplicação é fechada. Segue abaixo:

[code]package com.example.pi_android;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.SimpleCursorAdapter;

public class Tela1 extends Activity implements OnClickListener {
Intent it;
Button btn;
ListView listview;
BaseDAO helper;

private SQLiteDatabase database;
private CursorAdapter dtaSource;

public static final String campos[] = {“Contato_Nome”,“Contato_Grupo”};

private static final int CADASTRO = 0;
private static final int GRUPOS = 1;
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.tela1);
    
    listview = (ListView) findViewById(R.id.list);
  //  btn = (Button) findViewById(R.id.add);
    //btn.setOnClickListener(this);
    
    
    helper = new BaseDAO(this);
    database = helper.getWritableDatabase();
    

    Cursor c = database.query("Contatos",campos,null,null,null,null,null);
 
 if (c.getCount() > 0){
	 
	 dtaSource = new SimpleCursorAdapter(this, R.layout.contato_row, c, campos,new int[] {R.id.txtNome,R.id.txtEndereco});
	 
	 listview.setAdapter(dtaSource);
 }



    
}[/code]

Esses são os erros:

11-28 03:43:59.171: W/KeyCharacterMap(324): No keyboard for id 0 11-28 03:43:59.171: W/KeyCharacterMap(324): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 11-28 03:48:18.561: W/KeyCharacterMap(358): No keyboard for id 0 11-28 03:48:18.561: W/KeyCharacterMap(358): Using default keymap: /system/usr/keychars/qwerty.kcm.bin 11-28 04:00:28.504: D/AndroidRuntime(394): Shutting down VM 11-28 04:00:28.504: W/dalvikvm(394): threadid=1: thread exiting with uncaught exception (group=0x40015560) 11-28 04:00:28.582: E/AndroidRuntime(394): FATAL EXCEPTION: main 11-28 04:00:28.582: E/AndroidRuntime(394): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.pi_android/com.example.pi_android.Tela1}: java.lang.IllegalArgumentException: column '_id' does not exist 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread.access$1500(ActivityThread.java:117) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.os.Handler.dispatchMessage(Handler.java:99) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.os.Looper.loop(Looper.java:123) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread.main(ActivityThread.java:3683) 11-28 04:00:28.582: E/AndroidRuntime(394): at java.lang.reflect.Method.invokeNative(Native Method) 11-28 04:00:28.582: E/AndroidRuntime(394): at java.lang.reflect.Method.invoke(Method.java:507) 11-28 04:00:28.582: E/AndroidRuntime(394): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839) 11-28 04:00:28.582: E/AndroidRuntime(394): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597) 11-28 04:00:28.582: E/AndroidRuntime(394): at dalvik.system.NativeStart.main(Native Method) 11-28 04:00:28.582: E/AndroidRuntime(394): Caused by: java.lang.IllegalArgumentException: column '_id' does not exist 11-28 04:00:28.582: E/AndroidRuntime(394): at android.database.AbstractCursor.getColumnIndexOrThrow(AbstractCursor.java:314) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.widget.CursorAdapter.init(CursorAdapter.java:111) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.widget.CursorAdapter.<init>(CursorAdapter.java:90) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.widget.ResourceCursorAdapter.<init>(ResourceCursorAdapter.java:47) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.widget.SimpleCursorAdapter.<init>(SimpleCursorAdapter.java:84) 11-28 04:00:28.582: E/AndroidRuntime(394): at com.example.pi_android.Tela1.onCreate(Tela1.java:48) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 11-28 04:00:28.582: E/AndroidRuntime(394): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 11-28 04:00:28.582: E/AndroidRuntime(394): ... 11 more 11-28 04:00:37.082: I/Process(394): Sending signal. PID: 394 SIG: 9

O que poderia ser?