No overload matches delegate?

Question

Windows phone

I created a UserControl with several elements on it - the problem is with the button, or rather with the delegate:

public delegate void NotifyCallUserHelpPageEventHandler(string settingName);

        public event NotifyCallUserHelpPageEventHandler CallUserHelpPage;

        protected virtual void OnCallUserHelpPage()
        {
            NotifyCallUserHelpPageEventHandler handler = CallUserHelpPage;
            if (handler != null) handler(Header);
        }
//Событие нажатия на кнопку
        private void HelpButtonClick(object sender, RoutedEventArgs e)
        {
            OnCallUserHelpPage();
        }

so the control is inserted on the page

<controls:ToggleSwitchWithHelp 
                        Header="Использование местонахождения"
                        IsChecked="{Binding IsAllowUseMyGeopositionSetting, Converter={StaticResource SettingsConverter}, Mode=TwoWay, Source={StaticResource AppSettings}}" 
                        CallUserHelpPage="ToggleSwitchWithHelp_OnCallUserHelpPage"/>

and not being processed yet.

private void ToggleSwitchWithHelp_OnCallUserHelpPage(string settingName)
        {
            
        }

The compiler claims that there is no suitable delegate overload, but the error message is weird, like it's not completely finished. To tell the truth I do not know, what redefinition is necessary and where it is necessary to redefine.