.Resource does not contain a definiton for 'id'

using System;
using Android.App;
using Android.Content;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using Android.OS;

namespace kolko_i_krzyzyk
{
[Activity(Label = "Kółko i Krzyżyk", MainLauncher = true, Icon = "@drawable/icon")]
public class MainActivity : Activity
{
string tura = "krzyzyk";

    protected override void OnCreate(Bundle bundle)
    {
        base.OnCreate(bundle);
        SetContentView(Resource.Layout.Main);
        Button button1 = FindViewById<Button>(Resource.Id.button1);
    }
}

}

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

<Button

    p1:layout_width="127dp"
    p1:layout_height="100dp"
    p1:id="@+id/button1"
    p1:textSize="@android:dimen/app_icon_size" />

[...]

Where is my fault ? Why 'Kolko_i_krzyzyk.Resource' does not contain a definiton for 'id' ?