Unable to launch my app on ios simulator with xamarin studio

Hello,

I have a problem when I try to launch my app on ios simulator.

The build works perfectly but when I launch it, it crash at the start in the app delegate on "LoadApplication(new App());"

And i get the error : "object reference not set to an instance of an object"

Any idea what does it mean ?

In the upper left select box i chose "Debug | iPhoneSimulator" and it make my PCL solution greyish and says that the project is not built in active configuration ... is this the problem ? and if it is how do i start my app on iPhoneSimulator ?

Is it possible that i have a problem with the localization ?

this is my Localize file in iOS :

[assembly:Dependency(typeof(****.iOS.Localize))]
    namespace ****.iOS {
        public class Localize : ****.ILocalize {
            public System.Globalization.CultureInfo GetCurrentCultureInfo () {
                var netLanguage = "en";
            if (NSLocale.PreferredLanguages.Length > 0) {
                var pref = NSLocale.PreferredLanguages [0];
                netLanguage = pref.Replace ("_", "-");
            }
            return new System.Globalization.CultureInfo(netLanguage);
        }
    }
}

Thank you for your help !