An exception of type 'System.Reflection.TargetInvocationException'

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C#

Hi
I am trying to use date picker in my app but when i run the code in the emulator it shows the following error
"An exception of type 'System.Reflection.TargetInvocationException' occurred in Microsoft.Phone.ni.dll and wasn't handled before a managed/native boundary
The program '[2184] TaskHost.exe' has exited with code -1 (0xffffffff)."

This is my code below

public partial class MainPage : PhoneApplicationPage
    {
        Appointments appointments = new Appointments(); 
        
        // Constructor
        public MainPage()
        {
            InitializeComponent();

            appointments.SearchCompleted += new EventHandler<appointmentssearcheventargs>(appointments_SearchCompleted);
            SearchCalendar(); 

            // Sample code to localize the ApplicationBar
            //BuildLocalizedApplicationBar();
        }

        private void SearchCalendar()
        {
            appointments.SearchAsync(DateBox.Value.Value, DateBox.Value.Value.AddDays(1), null);
        }

        private void DateBox_ValueChanged(object sender, DateTimeValueChangedEventArgs e)
        {
            SearchCalendar();
        }

        void appointments_SearchCompleted(object sender, AppointmentsSearchEventArgs e)
        {
            if (e.Results.Count() == 0)
            {
                MessageText.Text = "no events for the selected day";
            }
            else
            {
                MessageText.Text = e.Results.Count() + " events found";
                DateList.ItemsSource = e.Results;
            }
        } 

Kindly help