Asp.net 我看到这个错误ORA-01722：当我想向oracle数据库表中插入数据时，编号无效

我想添加应答表，但看到类似“Oracle.DataAccess.Client.OracleException（0x80004005）：ORA-01722:无效数字”的错误

 DateTime localDate = DateTime.Now;
            var culture = new CultureInfo("ru-RU");
            var datenow = localDate.ToString(culture);
            string[] splitdatenow = datenow.Split(' ');    

 cnn.Open();
            OracleCommand cmdu = cnn.CreateCommand();
            cmdu.CommandText = "INSERT INTO ANSWER (EXPLAIN,STATUS,USERID,QUESTIONID,CREATEDATE,MEDIA) VALUES (:comment_forms,'T',(SELECT ID FROM USERS WHERE MAIL=:mailSession) ,:send,:datef,:uploadf)";
            cmdu.CommandType = CommandType.Text;
            cmdu.Parameters.Add(new OracleParameter(":send",OracleDbType.Int32));
            cmdu.Parameters.Add(new OracleParameter(":comment_forms", comment_form));
            cmdu.Parameters.Add(new OracleParameter(":datef", splitdatenow[0]));
            cmdu.Parameters.Add(new OracleParameter(":uploadf", upload_form));
            cmdu.Parameters[":gelenid"].Value = gel;
            cmdu.Parameters.Add(new OracleParameter(":mailSession",mailSession));
            try
            {
                cmdu.ExecuteNonQuery();
            }
            catch(Exception ex)
            {
                Response.Write(ex);
            }
            cnn.Close();

自动递增触发器

create or replace 
trigger ANSWERIDTRIGGER 
BEFORE INSERT ON ANSWER 
FOR EACH ROW 
BEGIN
  select ANSWERIDSEQ.nextval
        into :new.ID
        from dual;
END;

---

我更改了cmdu.Parameters[“：gelenid”]。值=gel；到cmdu.Parameters[“：send”]。值=凝胶；但ıt不插入表中，而gel是一个数字。请显示所讨论表的定义。