ORA-06502: PL/SQL: numeric or value error: character string buffer too small exception from C# code

I am trying to execute some oracle pl/sql procedure with in and out parameters from # code on asp.net. I want to retrive the value from out parameter. but when I execute i am getting a oracle exception like "ORA-06502: PL/SQL: numeric or value error: character string buffer too small".What can I do now? Please help me.

code:

using Oracle.DataAccess.Client;
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Activity.Account
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            SuccessLabel.Visible = false;
            FailureLabel.Visible = false;
        }

        protected void Create_user(object sender, EventArgs e)
        {
            var id="";
            string oradb = "Data Source=OracleServerHost;User ID=scott;password=tiger";
            using (OracleConnection conn = new OracleConnection(oradb))
            {
                try
                {
                    OracleCommand cmd = new OracleCommand();
                    cmd.Connection = conn;
                    cmd.CommandText = "create_users_372640";
                    cmd.CommandType = CommandType.StoredProcedure;
                    OracleParameter p1 = new OracleParameter("u_user_id", UserIDTextBox.Text.TrimEnd());
                    OracleParameter p2 = new OracleParameter("u_First", FirstNameTextBox.Text.TrimEnd());
                    OracleParameter p3 = new OracleParameter("u_Last", LastNameTextBox.Text.TrimEnd());
                    OracleParameter p4 = new OracleParameter("u_Email", EmailIDTextBox.Text.TrimEnd());
                    OracleParameter p5 = new OracleParameter("u_password", PasswordTextBox.Text.TrimEnd());
                    cmd.Parameters.Add(p1);
                    cmd.Parameters.Add(p2);
                    cmd.Parameters.Add(p3);
                    cmd.Parameters.Add(p4);
                    cmd.Parameters.Add(p5);
                    OracleCommand cmd_chk = new OracleCommand();
                    cmd_chk.Connection = conn;
                    cmd_chk.CommandText = "check_user_372640";
                    cmd_chk.CommandType = CommandType.StoredProcedure;
                    OracleParameter p6 = new OracleParameter("user_id", UserIDTextBox.Text.TrimEnd());
                    cmd_chk.Parameters.Add(p6);
                    cmd_chk.Parameters.Add("id", OracleDbType.Varchar2).Direction = ParameterDirection.Output;
                    conn.Open();
                    cmd_chk.ExecuteNonQuery();
                    id=(string)cmd_chk.Parameters["id"].Value;
                    //OracleDataReader rd = cmd_chk.ExecuteReader();
                    if (id != null && id != "")
                    {
                        //rd.Read();
                        SuccessLabel.Visible = false;
                        FailureLabel.Visible = true;
                    }
                    else
                    {
                        cmd.ExecuteNonQuery();
                        SuccessLabel.Visible = true;
                        FailureLabel.Visible = false;    
                    }
                }catch(Exception){
                    Console.WriteLine("SQL Exception Occured");
                }
            }

        }
    }
}

My oracle procedure is:

create or replace procedure check_user_372640(
user_id in varchar2,
id out varchar2
)
as
u_id varchar2(20);
begin
select user_id into u_id from ACTIVITY_USERS_372640 where user_id=user_id;
id:=u_id;
end;