hi.. i m gettin Exception as "public void alreadyExists() // function to check the existing records"

public void alreadyExists()    // function to check the existing records
    {
        DateTime tdy = DateTime.Now;
        DateTime aft2dy = DateTime.Now.AddDays(2);

        string str="select due_date from mConfirm where due_date BETWEEN '"+tdy+"' AND '"+aft2dy+"'";

        sda = new SqlDataAdapter(str, cn);
        ds1 = new DataSet();
        sda.Fill(ds1);    // HERE I M GETTING THE EXCEPTION.... AS
                           //"public void alreadyExists()    // function to check the existing records"

        string d = ds1.Tables[0].Rows[0].ItemArray[0].ToString();
        if ((Convert.ToDateTime(d) - DateTime.Today).TotalDays <= 2)    // HERE WHAT SHOULD I DO
        {
            LblAlreadyExists.Text = "Already Under Process";
        }



    }