Cannot find table at position 1 error

Question

I have a main form which has an Add Teacher button and an Add subject button which directs them to their respective forms.The add teacher button works perfectly fine but when i click the add subject button it shows error: Cannot find table at position 1.I have been following the same procedure in add subject button as i did in add teacher button .Also I first added tbl_teachers table and then tbl_subjects table in my database ,so technically tbl_teachers should have index 0 right?Also when i click the Data Source section I only see it has only tbl_teachers.How do I update the data source? Thanks in advance.

try
{
    SubjectConnect = new DatabaseConnection();
    conString = Properties.Settings.Default.teachersConnectionString;

    SubjectConnect.connection_string = conString;
    SubjectConnect.sql = Properties.Settings.Default.SQL2;

    ds = SubjectConnect.GetConnection;
    Maxrows = ds.Tables[1].Rows.Count;
}
catch (Exception err)
{
    MessageBox.Show(err.Message,"error");
}

class DatabaseConnection
{

    private string sql_string;
    private string strCon;
    SqlDataAdapter da_1;

    public string sql
    {
        set { sql_string = value; }
    }

    public string connection_string
    {
        set { strCon = value; }
    }

    public DataSet GetConnection
    {
        get { return MyDataset(); }
    }

    private DataSet MyDataset()
    {
        SqlConnection con = new SqlConnection(strCon);
        con.Open();
        da_1 = new SqlDataAdapter(sql_string, con);
        DataSet dat_set = new DataSet();
        da_1.Fill(dat_set,"Table_data_1");
        con.Close();
        return dat_set;
    }

    public void UpdateDatabase(DataSet ds)
    {
        SqlCommandBuilder cb = new SqlCommandBuilder(da_1);
        cb.DataAdapter.Update(ds.Tables[0]);
    }
}