disable send to in computer. "NullReferenceException was unhandled"

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using Microsoft.Win32;
using System.Runtime.InteropServices;
using System.IO;

namespace Anticopy
{   
   
   
    public partial class Form1 : Form
    {
        // Import user32.dll to call logoff API
        [DllImport("user32.dll")]       
        public static extern int ExitWindowsEx(int uFlags, int dwReason);
       
        public void anticopy()
        {
            if (chkDragDrop.Checked == true)
            {
                DialogResult u;
                u = MessageBox.Show("To Activate \nLog Off Required Now", "Log Off", MessageBoxButtons.YesNo);
                //if user Press Yes
                if (u == DialogResult.Yes)
                {
                    try
                    {

                        //Registry Value Change for disabling drag drop
                        RegistryKey dd = Registry.CurrentUser.OpenSubKey("Control Panel\\Desktop", true);
                        dd.SetValue("DragHeight", "9999");
                        dd.SetValue("Dragwidth", "9999");

                        //Application Register Itself To Launch On Next Window Logon for one time only
                        string currentpath = Path.GetDirectoryName(Application.ExecutablePath);
                        RegistryKey startup = Registry.CurrentUser.OpenSubKey("Software\\Microsoft\\Windows\\CurrentVersion\\RunOnce", true);
                        startup.SetValue("anticopy", currentpath + "\\Anticopy.exe");

                        //Log Off Window
                        ExitWindowsEx(0, 0);
                    }
                    catch (Exception ui)
                    {
                        MessageBox.Show("" + ui);
                    }
                }
            }
            else
            {
                if (chkSendTo.Checked == true)
                    sendto ("disable");

                btnStop.Enabled = true;
                btnStart.Enabled = false;

                this.Hide();
                timer1.Enabled = true;
                NotifyMe();
                label1.Text = "Just Minimize Me or Stop";
            }


        }

        private void sendto(string stat)
        {   // try and catch: cause window-xp use "Send To" and Vista,Window7 Use "SendTo"

            try
            {
                RegistryKey sendto =
                Registry.ClassesRoot.OpenSubKey("AllFilesystemObjects\\shellex\\ContextMenuHandlers\\SendTo", true);
                if (stat == "disable")
                    sendto.SetValue(null, "");
                else
                    sendto.SetValue(null, "{7BA4C740-9E81-11CF-99D3-00AA004AE837}");
            }
            catch
            {
                RegistryKey sendto = Registry.ClassesRoot.OpenSubKey("AllFilesystemObjects\\shellex\\ContextMenuHandlers\\Send To", true);
                if (stat == "disable")
                    sendto.SetValue(null, ""); //this is where it says NullReferenceException was unhandled
                else
                    sendto.SetValue(null, "{7BA4C740-9E81-11CF-99D3-00AA004AE837}");
            }

        }

        private void NotifyMe()
        {

            TrayIcon.BalloonTipTitle = "Anticopy";
            TrayIcon.BalloonTipText = "Anticopy Running..";
            TrayIcon.ShowBalloonTip(1);
            TrayIcon.ContextMenuStrip = contextMenuStrip1;
        }
    
       
        public Form1()
        {
            InitializeComponent();

        }        
        
        private void start_Click(object sender, EventArgs e)
        {
            anticopy();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            btnStop.Enabled = false;
            try
            {
                RegistryKey dd = Registry.CurrentUser.OpenSubKey("Control Panel\\Desktop", true);
                string DragHeight = dd.GetValue("DragHeight").ToString();
                string Dragwidth = dd.GetValue("Dragwidth").ToString();
                if (DragHeight == "4" && Dragwidth == "4") { }

                else
                {//if Drag Height & Width has Not default value then reset to default value
                    dd.SetValue("DragHeight", "4");
                    dd.SetValue("Dragwidth", "4");
                    chkSendTo.Checked = true;
                    anticopy();
                    btnStart.Enabled = false;
                }
            }
            catch { MessageBox.Show("Run Me As Admin"); this.Close(); }
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
           Clipboard.Clear();
        }

        private void chkDragDrop_CheckedChanged(object sender, EventArgs e)
        {
            if (chkDragDrop.Checked == true)
            {
                label1.Text = "Logoff Required";
            }
            else
            {
                label1.Text = "";
            }
        }

        private void btnStop_Click(object sender, EventArgs e)
        {
            timer1.Enabled = false;
            sendto ("enable");
            btnStart.Enabled = true;
            btnStop.Enabled = false;
            label1.Text = "";
            MessageBox.Show("If Drag Drop Were Disable\nActivate On Next Window LogOn");
        }
  
        private void Form1_Resize(object sender, EventArgs e)
        {
                       if( WindowState == FormWindowState.Minimized)
            Hide();
        }
       
        private void MyNotify_DoubleClick(object sender, EventArgs e)
        {
            Show();
            WindowState = FormWindowState.Normal;

        }

        private void closeToolStripMenuItem_Click(object sender, EventArgs e)
        {
            TrayIcon.Dispose();
            Application.Exit();

        }

        private void restoreToolStripMenuItem_Click(object sender, EventArgs e)
        {
            Show();
            WindowState = FormWindowState.Normal;

        }
          
    }
}