Application_Error in global.asax

1] DAL 
using System;
using System.Collections.Generic;
using System.Text;
using System.Data;
using System.Data.OleDb;
using DataObjectLayer;

namespace DataAccessLayer
{
public class UserDAL
{
public int UserAuthenticated(UserObj User)
{
int retVal = 0;
OleDbConnection conn = new OleDbConnection(DBConn.GetDbConnection());
OleDbCommand comm = new OleDbCommand();
string sql = "Select * From [User_Master$] where UserId = '" + User.UserName + "' and Pasw = '" + User.Password + "'";
try
{
comm.Connection = conn;
conn.Open();
comm.CommandText = sql;
comm.CommandType = CommandType.Text;

retVal = Convert.ToInt32(comm.ExecuteScalar());
conn.Close();
}
catch (Exception ex)
{
throw;
}
return retVal;
}
}
}




2] Global.asax


<%@ Application Language="C#" %>






my problem is when exception in occurs in DAL it cant show me Error.aspx which i mentioned in global.asax..please help me