VS2005 C#连接一个SQL SERVER数据库，程序运行报错 无法建立数据连接：实例失败。这是小弟我照书编写的第一个程序，卡壳4天了，求各位帮帮小弟我，不胜感激

VS2005 C#连接一个SQL SERVER数据库，程序运行报错 无法建立数据连接：实例失败。这是我照书编写的第一个程序，卡壳4天了，求各位帮帮我，不胜感激！
奇怪的是我的程序在别人的电脑里运行没问题，可到我这就报错，点击登陆界面的前三个按钮想跳到其他三个界面，都报这样的错误。第四个按钮能跳转到另一个界面，我的第四个界面是用报表实现的，我的app.configure
<connectionStrings>
  <add name="Explore700Store.Properties.Settings.Explore700StoreConnectionString"  
  connectionString="Data Source=.\\SQLEXPRESS;Initial Catalog=Explore700Store;Integrated Security=True;
  AttachDbFilename=C:\Program Files\Microsoft SQL Server\MSSQL.1\MSSQL\DATA;" providerName="System.Data.SqlClient" />
  </connectionStrings>
第一个界面（登陆界面）的代码：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Configuration;

namespace WindowsApplication1
{
  public partial class Form1 : Form
  {
  protected SqlConnection conn;
  protected SqlCommand cmd;
  protected Explore700StoreDataSetTableAdapters.Explore700TableAdapter adapter;
  public Form1()
  {
  InitializeComponent();
  }
   
  private void button1_Click(object sender, EventArgs e)
  {
  Explore700Form frm1=new Explore700Form();
  frm1.Show();
  this.Visible = false;
  }

  private void button2_Click(object sender, EventArgs e)
  {
  CustomerForm frm1 = new CustomerForm();
  frm1.Show();
  this.Visible = false;
  }

  private void Form1_Load(object sender, EventArgs e)
  {

  }

  private void button3_Click(object sender, EventArgs e)
  {
  SellForm frm1 = new SellForm();
  frm1.Show();
  this.Visible = false;
  }

  private void button4_Click(object sender, EventArgs e)
  {
  ReportForm frm1 = new ReportForm();
  frm1.Show();
  this.Visible = false;
  }
  }
}
第二个界面的部分代码：
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Configuration;


namespace WindowsApplication1
{
  public partial class CustomerForm : Form
  {
  protected SqlConnection conn;
  protected SqlCommand cmd;
  public CustomerForm()
  {
  InitializeComponent();
  }

  private void CustomerForm_Load(object sender, EventArgs e)
  {
  try
  {
  SqlConnectionStringBuilder sb1=new SqlConnectionStringBuilder ();
  sb1 .DataSource ="(Local)";
  sb1 .InitialCatalog ="Explore700Store";
  sb1 .IntegratedSecurity =true ;
  conn = new SqlConnection(sb1 .ConnectionString);
  cmd = new SqlCommand();
  cmd.Connection = conn;
  conn.Open();
  this.InitData();
  }
  catch (Exception exp)
  {
  MessageBox.Show("无法建立数据连接：" + exp.Message);