[Silverlight] MessageBox Black Page

Question

I do Silverlight MVC project on VWDEE2010

when I do

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        MessageBox.Show("I am a button");
    }

Message shows on BlackScreen on background and only when I click OK it returnts me to my page. Why black page and what ways to avoid ?

Thank you.