Don't find activity

Hi.
I don't know if this is the right forum or I should move the thread in "Android" forum.

This is the situation:
I have a PCL "Xamarin Forms" Project with a "Android" Project.
The "Android" project has 2 activity.
- a Splash activity very simple that "popup" a splash screen and call the "MainActivity"

    [Activity(
    Icon = "@drawable/icon", 
    Label = "FEV",
    Theme = "@style/Theme.Splash", 
    MainLauncher = true, 
    ScreenOrientation = ScreenOrientation.Portrait,
    NoHistory = true)]
public class SplashActivity : Activity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        base.OnCreate(savedInstanceState);
        StartActivity(typeof(MainActivity));
    }
}}

• the MainActivity that "Runs" the app.

Ok, it works!.

Now I have to change the MainActivity from

    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity

to

public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsApplicationActivity, EMDKManager.IEMDKListener

because I have to implement some code for Symbol / Motorola Scanner etc etc etc

If I change this line of code, I have this exception

java.lang.ClassNotFoundException: Didn't find class "md56c8c3f80e969d580e31249f73c358691.MainActivity"

If I remove

, EMDKManager.IEMDKListener

the exception is not thrown.

Any suggestion?

Thanks