Unable to take databse backup

using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        //Metioned here your database name
        string dbname = "test1";
        SqlConnection sqlcon=new SqlConnection();
        SqlCommand sqlcmd = new SqlCommand();
        SqlDataAdapter da = new SqlDataAdapter();
        DataTable dt = new DataTable();

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
    
            //Mentioned Connection string make sure that user id and password sufficient previlages
            sqlcon.ConnectionString = @"Server=RAVI-PC\SQLEXPRESS;database=" + dbname + ";uid=ravindran;pwd=srirangam;";

            //Enter destination directory where backup file stored
            string destdir = "D:\\backupdb";

            //Check that directory already there otherwise create
            if (!System.IO.Directory.Exists(destdir))
            {
                System.IO.Directory.CreateDirectory("D:\\backupdb");
            }
            try
            {
                //Open connection
                sqlcon.Open();
                //query to take backup database
                sqlcmd = new SqlCommand("backup database  " + dbname + " to disk='" + destdir + "\\" + DateTime.Now.ToString("ddMMyyyy_HHmmss") + ".Bak'", sqlcon);
                sqlcmd.ExecuteNonQuery();
                //Close connection
                sqlcon.Close();
               MessageBox.Show("Backup database successfully");
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error During backup database!");
            }
        }
    }
}

Getting Error During backup database!