title: Xamarin does not recognise any project anymore
body: <p>Today I was working on several projects and nothing wrong. Suddenly Xamarin does not understand any project anymore. Nothing changed at all. It just says I'm making errors.</p>
  
  <pre><code>using Android.OS;       
  using Android.App;     
  using Android.Widget;   
  using Android.Graphics; 
  
  [ActivityAttribute(Label = "Hello", MainLauncher = true)]
  public class HelloApp : Activity
  {
  protected override void OnCreate(Bundle b)
  {
      MainActivity.OnCreate(base, b);
  
      TextView screen;
      screen = new TextView(this);
      screen.Text     = "Hello!";
      screen.TextSize = 80;
      screen.SetBackgroundColor(Color.Yellow);
      screen.SetTextColor      (Color.DarkBlue);
  
      this.SetContentView(screen);
      }
  }
  </code></pre>
  
  <p>so 'b' parameter name differs in base declaration. The name name 'MainActivity' does not exist in the current context. Use of the keyword 'base' is not valid in this context.</p>
  
  <p>It doesn't matter what I make, what (what was working) project I am in. Nothing works anymore. Has anyone got any idea what went wrong?</p>