C#链接SQL Server 2005的问题

Web server, SQL Server都在本机上。
连接语句如下：
SqlConnection conn;
conn= new SqlConnection("server=192.168.11.3;database=TestDb;uid=TestDb_Admin;pwd=123456789");
conn.Open();

奇怪的是，如果是一个C#, WinForm的程序，这个链接可以成功，并且已经可以INSERT数据到表里了。

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Data;

using System.Data.SqlClient;

using System.Drawing;

using System.Linq;

using System.Text;

using System.Windows.Forms;



namespace WindowsFormsApplication1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }



        private void button1_Click(object sender, EventArgs e)

        {

           SqlConnection conn;  

           conn= new SqlConnection("server=192.168.11.3;database=TestDb;uid=TestDb_Admin;pwd=123456789"); 

           conn.Open();

但是，如果是在Web上面，同样的

           SqlConnection conn;  

           conn= new SqlConnection("server=192.168.11.3;database=TestDb;uid=TestDb_Admin;pwd=123456789"); 

           conn.Open();

报告错
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)
这是为什么？