IDataErrorInfo in Multiple View Models

hi,

Here is my Sample Code:

ViewModel:

        private string firstName;
        public string FirstName
        {
            get { return firstName; }
            set { firstName = value; OnPropertyChanged("FirstName"); }
        }
.................
..................

InfoViewModel:

        private string lastName;
        public string LastName
        {
            get { return lastName; }
            set { lastName = value; OnPropertyChanged("LastName"); }
        }

        private string getFirstName;
        public string GetFirstName
        {
            get { return getFirstName; }
            set { getFirstName = value; OnPropertyChanged("GetFirstName"); }
        }

MainWindow.Xaml:

       ViewModel viewModel = new ViewModel();
        public InfoViewModel infoChildView = new InfoViewModel();
        Window1 window1 = new Window1();

        public MainWindow()
        {
            InitializeComponent();
            DataContext = viewModel;
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            if (!viewModel.IsValid())
            {
                MessageBox.Show("Error Message");
            }
            else
            {window1.DataContext = infoChildView;//To Window1
                infoChildView.GetFirstName = viewModel.FirstName;
                window1.Show();
            }
<TextBox Text="{Binding FirstName, ValidatesOnDataErrors=True}" />
<Button Content="Button"Click="Button_Click"/>

Window1.Xaml:

        public MainWindow mainWindow;
        InfoViewModel infoChildView = new InfoViewModel();

        public Window1()
        {
            InitializeComponent();
        }

        private void Done_Click(object sender, RoutedEventArgs e)
        {
            if (!infoChildView.IsValid())
            {
                MessageBox.Show("Error Message");
            }
            else
            {
                MessageBox.Show("Good To go");
            }
        }
<TextBlock Text="{Binding GetFirstName}" />
<TextBox Text="{Binding LastName, ValidatesOnDataErrors=True}"/>
<Button Content="Done" Click="Done_Click"/>

I have already made IDataErrorInfo in both view model (ViewModel and InfoViewModel). The mainWindow is fine but my problem is that  I cannot see validation error message in window1 when i clicked Done_Click event if textbox is empty. i think i already DataContext in MainWindow called through a window1.

Am i missing DataContext in window1? Any idea?

Thanks