newtonsoft.json.jsonreaderexception: unexpected character encountered while parsing value: e. path '

newtonsoft.json.jsonreaderexception: unexpected character encountered while parsing value: e. path '', line 0, position 0.

I got the error message.

public class TabPageControl : Xamarin.Forms.TabbedPage
 {

    public TabPageControl()
    {

        On<Xamarin.Forms.PlatformConfiguration.Android>().SetToolbarPlacement(ToolbarPlacement.Bottom);

        Children.Add(new Showcase());
        Children.Add(new Explore());
        Children.Add(new NotificationTabControl());
        Children.Add(new Profile());

        NavigationPage.SetHasNavigationBar(this, false);

 }

private async void Button_Clicked(object sender, EventArgs e)
    {
        await Navigation.PushAsync(new TabPageControl());
    }

When I change the TabPageControl page with Showcase page, I don't get error.

Please help me.