BroadcastReceiver Force to close app android

I am wanting to check the status of my Wifi/3G connection, but when my application is closed when I lose my signal connection. I use a code found on the network as an example. Tested in the emulator and when I take the 3G connection the app is forced to close. this code is simple and got the logs.

Log ERROR: http://img826.imageshack.us/img826/2389/hmjz.png

public class Activity1 : Activity
{
    int count = 1;

    public static TextView txtNote;

    static string teste2;

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);

        // Set our view from the "main" layout resource
        SetContentView(Resource.Layout.Main);

        // Get our button from the layout resource,
        // and attach an event to it
        Button button = FindViewById<Button>(Resource.Id.MyButton);

        txtNote = FindViewById<TextView>(Resource.Id.textView1);

        button.Click += delegate { button.Text = string.Format("{0} clicks!", count++); };

    }

    protected override void OnResume()
    {
        base.OnResume();

        IntentFilter mIFNetwork = new IntentFilter();
        mIFNetwork.AddAction(Android.Net.ConnectivityManager.ConnectivityAction);
        RegisterReceiver(new NetworkChangeReceiver(), mIFNetwork);
    }

    public class NetworkChangeReceiver : Android.Content.BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)

        {

            String status = AndroidApplication10.Resources.NetworkUtil.getConnectivityStatusString(context);

            Toast.MakeText(context, status, ToastLength.Long).Show();
        }
    }
}

}

Other Class:

public class NetworkUtil { public static int TYPE_WIFI = 1; public static int TYPE_MOBILE = 0 ; public static int TYPE_NOT_CONNECTED = 3;

    public static int getConnectivityStatus(Context context)
    {
        ConnectivityManager cm = (ConnectivityManager)context
                .GetSystemService(Context.ConnectivityService);

        NetworkInfo activeNetwork = cm.GetNetworkInfo(ConnectivityType.Mobile);

        int teste = (int) activeNetwork.Type;

        if (null != activeNetwork)
        {
            if (teste == NetworkUtil.TYPE_WIFI)
                return TYPE_WIFI;

            if (teste == NetworkUtil.TYPE_MOBILE)
                return TYPE_MOBILE;
        }
        return TYPE_NOT_CONNECTED;
    }

    public static String getConnectivityStatusString(Context context)
    {
        int conn = NetworkUtil.getConnectivityStatus(context);
        String status = null;
        if (conn == NetworkUtil.TYPE_WIFI)
        {
            status = "Wifi enabled";
        }
        else if (conn == NetworkUtil.TYPE_MOBILE)
        {
            status = "Mobile data enabled";
        }
        else if (conn == NetworkUtil.TYPE_NOT_CONNECTED)
        {
            status = "Not connected to Internet";
        }
        return status;
    }
}