I CANT FIX PLEASE HELP-An exception of type 'System.IO.FileNotFoundException' occurred in xmppStart.exe but was not handled in user code

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C#

X++

Windows-Phone-8.1

Here i am trying to develop a chat app using xmpp and openfire server in windows phone 8.1.when i am trying to connect with openfire server it showing this error.i tried out many ways but no result and i cannot understand too..(i added username and password in server)

this part am getting error-

ObjXmppClient = new XMPPClient();

An exception of type 'System.IO.FileNotFoundException' occurred in xmppStart.exe but was not handled in user code

Additional information: Could not load file or assembly 'System.Windows, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e' or one of its dependencies. The system cannot find the file specified.

my code is given below [If it is not the way to connect server using xmpp pls let me know]

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Navigation;
using System.Net.XMPP;
using System.Threading;
using Windows.UI.Popups;


namespace xmppStart
{
    public sealed partial class MainPage : Page
    {



        public XMPPClient ObjXmppClient { get; set; }
        public XMPPConnection ObjXmppCon { get; set; }
        public string username = "sree";
        public string password = "sree";
        public readonly string server = "taurus";
        private Boolean IsXmppSuccess { get; set; }
 
        public MainPage()
        {
            this.InitializeComponent();

            this.NavigationCacheMode = NavigationCacheMode.Required;
        }

      
        private void IsXmppValid()
        {
          
            //initializing the xmpp client with credentials
            ObjXmppClient = new XMPPClient();
            ObjXmppClient.JID = username + "@" + server;
            ObjXmppClient.Password = password;
            ObjXmppClient.Server = server;  //user server for emulator and ip address for device.
            ObjXmppClient.AutoReconnect = true;
            ObjXmppClient.RetrieveRoster = true;
            ObjXmppClient.PresenceStatus = new PresenceStatus() { PresenceType = PresenceType.available, IsOnline = true };
            ObjXmppClient.AutoAcceptPresenceSubscribe = true;
            ObjXmppClient.AttemptReconnectOnBadPing = true;
            ObjXmppCon = new XMPPConnection(ObjXmppClient);
            ObjXmppCon.Connect();
            ObjXmppClient.Connect();

            //initializing the xmpp connection

            ObjXmppCon.OnAsyncConnectFinished += ObjXmppCon_OnAsyncConnectFinished;
            ObjXmppClient.OnStateChanged += new EventHandler(xMPPClient_OnStateChanged);
         
        }

        void ObjXmppCon_OnAsyncConnectFinished(xmedianet.socketserver.SocketClient client, bool bSuccess, string strErrors)
        {
            IsXmppSuccess = client.Connected;
        }


        public async void xMPPClient_OnStateChanged(object sender, EventArgs e)
        {
            switch (ObjXmppClient.XMPPState)
            {
                case XMPPState.Ready:


                    if (IsXmppSuccess)
                    {


                        await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
                        {


                            Frame.Navigate(typeof(Logedin));


                        });
                    }

                    else
                    {

                        await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
                        {


                            MessageDialog msgbox = new MessageDialog("Check server name/IpAddress");


                        });


                    }
                    break;

                case XMPPState.AuthenticationFailed: await Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
                {


                    MessageDialog msgbox = new MessageDialog("Enter valid username and password");


                    return;

                }); break;
            }
        }



        protected override void OnNavigatedTo(NavigationEventArgs e)
        {
           
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            if (txtname.Text == string.Empty)
            {
                MessageDialog msgbox = new MessageDialog("enter user name");
                return;
            }
            if (txtpassword.Text == string.Empty)
            {
                MessageDialog msgbox = new MessageDialog("enter password");
                return;
            }

            username = txtname.Text;
            password = txtpassword.Text;
            IsXmppValid();
        }
    }
}