Error CS1061: AppDelegate does not contain a definition for GetNativeField

I'm writting my first iPhone app using mono touch. I have only written a little bit of code, and suddenly, it does not compile anymore, I get this error:

/MyRoute/MainWindow.xib.designer.cs(85,85): Error CS1061: Type xxxx.AppDelegate' does not contain a definition forGetNativeField' and no extension method GetNativeField' of typexxx.AppDelegate' could be found (are you missing a using directive or an assembly reference?) (CS1061) (xxx)

Any idea where this error comes from and how to solve it?

Thanks! :-D

Edited: Added aditional information:

THIS IS THE MAINWINDOW DESIGNER CODE:

namespace GuiaTeleIphone {


    // Base type probably should be MonoTouch.Foundation.NSObject or subclass
    [MonoTouch.Foundation.Register("AppDelegate")]
    public partial class AppDelegate {

        private MonoTouch.UIKit.UIWindow __mt_window;

        #pragma warning disable 0169
        [MonoTouch.Foundation.Connect("window")]
        private MonoTouch.UIKit.UIWindow window {
            get {
                this.__mt_window = ((MonoTouch.UIKit.UIWindow)(this.GetNativeField("window")));
                return this.__mt_window;
            }
            set {
                this.__mt_window = value;
                this.SetNativeField("window", value);
            }
        }
    }
}

THIS IS THE MAIN.CS:

namespace GuiaTeleIphone
{
    public class Application
    {
        static void Main (string[] args)
        {
            UIApplication.Main (args);
        }
    }

    // The name AppDelegate is referenced in the MainWindow.xib file.
    public partial class AppDelegate : UIApplicationDelegate
    {
        List<RSSChannel> RemoteChannelsData;

        // This method is invoked when the application has loaded its UI and its ready to run
        public override bool FinishedLaunching (UIApplication app, NSDictionary options)
        {
            // If you have defined a view, add it here:
       开发者_开发知识库     // window.AddSubview (navigationController.View);

            window.MakeKeyAndVisible ();

                        // do things here

            return true;
        }

        }
}

The other partial class of xxxx.AppDelegate is missing or in a different namespace. It specifies the base class.