索引超出了允许的范围.为什么?

我的C#代码有问题，我无法解决这个问题。所以，我的问题是，当我尝试登录时会出现异常。没有任何固定元素对象。代码中的问题在哪里？例外：

索引超出了允许的范围。参数：索引

代码：

    public dbresult.GetSome Get(Oneword.dbcon conn, string tablename) {
        string constring = "Server=" + conn.Host + ";Database=" + conn.Database + ";Uid=" + conn.Username + ";Pwd=" + conn.Password;
        int i,im=0;
        Oneword.dbresult.GetSome result = new dbresult.GetSome();
        MySqlConnection connection = new MySqlConnection(constring);
        connection.Open();
        try {
            MySqlDataReader oszlopok_cmd = null;
            MySqlDataReader sorok_cmd = null;
            DataTable oszlopok = null;
            MySqlCommand cmd = connection.CreateCommand();
            cmd.CommandText = "SELECT * FROM "+tablename;
            // Oszlopok lekérése
            oszlopok_cmd = cmd.ExecuteReader(CommandBehavior.SchemaOnly);
            oszlopok = oszlopok_cmd.GetSchemaTable();
            oszlopok_cmd.Close();
            List<string> columns = new List<string>();
            foreach (DataRow col in oszlopok.Rows) {
                columns.Add(col.Field<String>("ColumnName"));
            }
            // Sorok lekérése, és tárak feltöltése
            sorok_cmd = cmd.ExecuteReader();
            while (sorok_cmd.Read()) {
                i = result.AddNewDir();
                foreach (string clomone in columns) {
                    result.AddKeyValue(i, clomone, sorok_cmd.GetString(im));
                    im++;
                }
            }
        }
        finally {
            connection.Close();
        }
        return result;
    }
public class dbresult {
    public class GetSome {
        private List<Dictionary<string, string>> dirlistem = new List<Dictionary<string, string>>();
        private int cuID = 0;
        public void AddKeyValue(int dirID, string key, string value){
            dirlistem[dirID][key] = value;
        }
        public int AddNewDir() {
            Dictionary<string,string> added = new Dictionary<string,string>();
            cuID++;
            return cuID - 1;
        }
        public Dictionary<string, string> GetDir(int dirID) {
            return dirlistem[dirID];
        }
        public void ModifyValue(int dirID, string key, string value) {
            dirlistem[dirID][key] = value;
        }
    }
}

public int AddNewDir() {
  Dictionary<string,string> added = new Dictionary<string,string>();
  // ***
  dirlistem.Add(added);
  // ***
  cuID++;
  return cuID - 1;
}

return dirlistem.Count - 1;