لماذا يظهر هذا الخطأ في DataRow

SqlConnection sqlconn1 = new SqlConnection(connstr);

string commandString = "SELECT * FROM TableName";

SqlDataAdapter adapter = new SqlDataAdapter(commandString, sqlconn1);

System.Data.DataSet ds = new System.Data.DataSet();

System.Data.DataTable dt = new System.Data.DataTable();

System.Data.DataRow row= new System.Data.DataRow(); الخطا يظهر هنا<<(System.Data.DataRowBuilder)' is inaccessible due to its protection level

row = dt.NewRow();

dt = ds.Tables["TableName"];

sqlconn1.Open();

row = ds.Tables["TableName"].NewRow();

totalRec = dt.Rows.Count;

curRec = totalRec - 1;

row = dt.Rows[curRec];

row["col1"] = totalRec;

row["col2"] = TchName.Text;

row["col3"] = Tchpass.Text;

ds.Tables["TableName"].Rows.Add(row);

ds.AcceptChanges();

adapter.Update(ds, "TableName");

sqlconn1.Close();