VB登陆代码的问题

错误：连接无法用于执行此操作，在此上下文中它可能已被关闭或效
提示在：str.Open strSQl, conn, 3, 2

哪位大哥能帮帮小弟，谢谢了

Public conn As ADODB.Connection
Sub main()
    Set conn = New ADODB.Connection
     conn.ConnectionString = "Provider=SQLOLEDB.1;Persist Security Info=True;User ID=sa;Initial Catalog=lianxi;Data Source=."
     conn.Open
     from1.Show     '登录界面
End Sub
Private Sub Command1_Click()
     If Text1.Text = "" Then
        MsgBox "用户名不能为空！", vbOKOnly + vbInformation, "友情提示"
        Text1.SetFocus
        Exit Sub
    End If
    If Text2.Text = "" Then
        MsgBox "密码不能为空！", vbOKOnly + vbInformation, "友情提示"
        Text2.SetFocus
        Exit Sub
    End If
     Dim strSQl As String
     strSQl = "select * from user where username='" & Trim$(Text1.Text) & "' and password='" & Trim$(Text2.Text) & "' "
     Dim str As New ADODB.Recordset
     Set str = New ADODB.Recordset
     str.CursorLocation = adUseClient
     str.Open strSQl, conn, 3, 2
        If str.EOF = True Then
            MsgBox "对不起，用户名不存在或密码错误！", vbOKOnly + vbQuestion, "警告"
                Text1.SetFocus
                Text1.Text = ""
                Text2.Text = ""
        Else
            MsgBox "欢迎使用本系统！", vbOKOnly + vbInformation, "友情提示"
            Unload Me
            Form2.Show    '登录进入的另一个界面
        End If
  End Sub

补充：VB ,  数据库(包含打印，安装，报表)