如何在vb 2012中连接数据库

Question

Imports System.Data

Imports System.Data.SqlClient

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim conStr As String = "Data Source=.\SQLEXPRESS;AttachDbFilename='C:\Users\Pode\Documents\Visual Studio 2012\Projects\Northwind.mdf';Integrated Security=True;User Instance=True"
        Dim conn As New SqlConnection(conStr)
        conn.Open()  
        MessageBox.Show("Success")
    End Sub
End Class

为何错误conn.Open()？