Runtime Exception AlertDialog в Android

Я пытаюсь выполнить следующий код ... но AlertDialog создает проблемы! Без этого код работает нормально. Я хочу, чтобы появилось диалоговое окно и попросило пользователя включить GPS, когда он выключен!

public class Testing extends Service {
    private Location loc;
    private Dialog dialog;
    String DATA;
    @Override
    public IBinder onBind(Intent arg0) {
        // TODO Auto-generated method stub
        return null;
    }
    @Override
    public void onCreate()
    {       
            super.onCreate();
    }
    @Override
    public void onStart(Intent intent, int startId) 
    {
        LocationManager LM = (LocationManager)getSystemService(Context.LOCATION_SERVICE);
        if (!LM.isProviderEnabled(LocationManager.GPS_PROVIDER)){ 
            AlertDialog.Builder builder = new AlertDialog.Builder(this);
            builder.setMessage("Your GPS is disabled! Would you like to enable it?")
                    .setCancelable(false).setPositiveButton("Enable GPS",
                            new DialogInterface.OnClickListener() {
                                public void onClick(DialogInterface dialog, int id) {
                                    Intent gpsOptionsIntent = new Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS);
                                    startActivity(gpsOptionsIntent);
                                }
                            });
            builder.setNegativeButton("Do nothing",
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            dialog.cancel();
                        }
                    });
            AlertDialog alert = builder.create();
            alert.show();
        }
        LocationListener LL = new MyLocationListener();
        LM.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 1000, 0, LL);
        LM.requestLocationUpdates(LocationManager.GPS_PROVIDER, 1000, 0, LL);
       /*//Runnable to determine when the first GPS fix was received.
        Runnable showWaitDialog = new Runnable() {
            @Override
            public void run() {
            while (loc == null) {
            // Wait for first GPS Fix (do nothing until loc != null)
            }
            // After receiving first GPS Fix dismiss the Progress Dialog
            dialog.dismiss();
            }
            };
            // Create a Dialog to let the User know that we're waiting for a GPS Fix
            dialog = ProgressDialog.show(getApplicationContext(), "Please wait...","Retrieving GPS data ...", true);
            Thread t = new Thread(showWaitDialog);
            t.start();*/
        LM.addNmeaListener(new NmeaListener() {
        public void onNmeaReceived(long timestamp, String nmea) 
        { 
                    DATA = nmea;
        }});
    }

Но я получаю эту ошибку! Код ProgressDialog в строках комментариев также вызывает ту же ошибку!

08-04 04:36:09.664: ERROR/AndroidRuntime(6301): FATAL EXCEPTION: main
08-04 04:36:09.664: ERROR/AndroidRuntime(6301): java.lang.RuntimeException: Unable to start service Firstdroid.Gps.Testing@462a35d0 with Intent { cmp=Firstdroid.Gps/.Testing }: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3282)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.ActivityThread.access$3600(ActivityThread.java:135)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2211)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.os.Looper.loop(Looper.java:144)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.ActivityThread.main(ActivityThread.java:4937)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at java.lang.reflect.Method.invokeNative(Native Method)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at java.lang.reflect.Method.invoke(Method.java:521)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at dalvik.system.NativeStart.main(Native Method)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301): Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an application
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.view.ViewRoot.setView(ViewRoot.java:513)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:177)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:91)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.Dialog.show(Dialog.java:241)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at Firstdroid.Gps.UrbanExplorer.onStart(UrbanExplorer.java:84)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.Service.onStartCommand(Service.java:420)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3267)
08-04 04:36:09.664: ERROR/AndroidRuntime(6301):     ... 10 more