vb.net2010和access登陆出错解决方案

vb.net2010和access登陆出错
 Private Sub login_btn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles login_btn.Click
        If UsernameTextBox.Text = "" Then
            MsgBox("用户名不能为空！请输入用户名。")
            UsernameTextBox.Focus()
        Else
            Dim cnn As New OleDbConnection
            cnn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Users\shen\Documents\Visual Studio 2010\Projects\溪洛渡垂线监测数据管理系统\溪洛渡垂线监测数据管理系统\cx.mdb"
            cnn.Open()
            Dim ds As New DataSet
            Dim da As New OleDbDataAdapter("select * from [user]", cnn)
            cnn.Close()
            da.Fill(ds, "user")
            If ds.Tables(0).Rows.Count <> 0 Then
                Dim sql As String = "select * from [user] where 用户名='" & Trim(UsernameTextBox.Text) & "' "
                Dim da1 As New OleDbDataAdapter(sql, cnn)
                Dim ds1 As New DataSet
                da1.Fill(ds1, "user")
                If ds1.Tables(0).Rows.Count = 0 Then
                    MsgBox("用户名错误！")
                    UsernameTextBox.Text = ""
                    UsernameTextBox.Focus()
                Else
                    If PasswordTextBox.Text = "" Then
                        MsgBox("请输入密码！")
                        PasswordTextBox.Focus()
                    Else
                        Dim sq2 As String = "select 密码  from [user] where 用户名='" & Trim(UsernameTextBox.Text) & "'and 密码 ='" & Trim(PasswordTextBox.Text) & "'"
                        Dim da2 As New OleDbDataAdapter(sql, cnn)
                        Dim ds2 As New DataSet
                        da2.Fill(ds2, "user")
                        If ds2.Tables(0).Rows.Count < 1 Then
                            MsgBox("密码错误！请重新输入密码！")
                            PasswordTextBox.Text = ""
                            PasswordTextBox.Focus()
                        Else
                            Me.Hide()
                            main_frm.Show()
                        End If