Please correct the error o session

for (int i = 0; i < GridView2.Rows.Count; i++)
        {
          
            string strID  = GridView2.Rows[i].Cells[1].Text;

    


            con.Open();
            using (SqlCommand command = new SqlCommand("select Role_Name from Role2 where Role_ID=@strID", con))
            { 
                SqlParameter param = new SqlParameter();
                param.ParameterName = "@StrID"; param.Value = strID;   
                command.Parameters.Add(param); 
                SqlDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    Session["Role_Name"] = Convert.ToString(reader["Role_Name"]);
                }

            }
            con.Close();
        }