i got the error "backup failed for Server 'XYZ-PC\\SQLEXPRESS'.how to resolve it

 public void button1_Click(object sender, EventArgs e)
        {
            try
            {

                //Define a Backup object variable.
                Backup sqlBackup = new Backup();

                //Specify the type of backup, the description, the name, and the database to be backed up.
                sqlBackup.Action = BackupActionType.Database;
                sqlBackup.BackupSetDescription = "BackUp of:" + "Garment.mdf" + "on" + DateTime.Now.ToShortDateString();
                sqlBackup.BackupSetName = "FullBackUp";
                sqlBackup.Database = "Garment.mdf";

                //Declare a BackupDeviceItem
                BackupDeviceItem deviceItem = new BackupDeviceItem("D:\\SQLBackup" + "Garment.bak", DeviceType.File);
                //Define Server connection
                ServerConnection connection = new ServerConnection(".\\SQLEXPRESS");
                //To Avoid TimeOut Exception
                Server sqlServer = new Server(connection);
                sqlServer.ConnectionContext.StatementTimeout = 60 * 60;
                Database db = sqlServer.Databases["Garment.mdf"];

                sqlBackup.Initialize = true;
                sqlBackup.Checksum = true;
                sqlBackup.ContinueAfterError = true;

                //Add the device to the Backup object.
                sqlBackup.Devices.Add(deviceItem);
                //Set the Incremental property to False to specify that this is a full database backup.
                sqlBackup.Incremental = false;

                sqlBackup.ExpirationDate = DateTime.Now.AddDays(3);
                //Specify that the log must be truncated after the backup is complete.
                sqlBackup.LogTruncation = BackupTruncateLogType.Truncate;

                sqlBackup.FormatMedia = false;
                //Run SqlBackup to perform the full database backup on the instance of SQL Server.
                sqlBackup.SqlBackup(sqlServer);
                //Remove the backup device from the Backup object.
                sqlBackup.Devices.Remove(deviceItem);

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }
}