无法打开备份设备'；D: 工作项目 FullBackUp.BAK'；.操作系统错误3(系统找不到指定

这个问题在Stackoverflow中得到了很多次回答，但我没有为我的项目找到合适的解决方案。

让我先给你看我的代码：

namespace ConsoleDBManagement
{
    class Program
    {
        static void Main(string[] args)
        {
            //Metioned here your database name
            string dbname = "newDb";
            SqlConnection sqlcon = new SqlConnection();
            SqlCommand sqlcmd = new SqlCommand();
            SqlDataAdapter da = new SqlDataAdapter();
            DataTable dt = new DataTable();
            sqlcon.ConnectionString = @"Server=ABC-PC'SQLEXPRESS;database=" + dbname + ";uid=dran;pwd=sri;";
            //Enter destination directory where backup file stored
            string destdir = "D:''Working Projects";
            //Check that directory already there otherwise create 
            if (!System.IO.Directory.Exists(destdir))
            {
               System.IO.Directory.CreateDirectory("D:''Working Projects");
            }
            try
            {
                //Open connection
                sqlcon.Open();
                //query to take backup database
                //System.IO.File.Create("D:''Working Projects''FullBackUp.BAK");
                sqlcmd = new SqlCommand("backup database newDb to disk='" + destdir + "''FullBackUp.BAK'", sqlcon);
                sqlcmd.ExecuteNonQuery();
                //Close connection
                sqlcon.Close();
                //Response.Write("Backup database successfully");
            }
            catch (Exception ex)
            {
                //Response.Write("Error During backup database!");
            }
        }
    }
}

执行查询时出现异常。

无法打开备份设备"D:''Working Projects''FullBackUp.BAK"。操作系统错误3（系统找不到指定的路径。）。

BACKUP DATABASE正在异常终止。

请给我你的建议。