我用下面代码实现登陆界面， 学号和密码是数字还能用，可一变成字母例如学号=zm就提示这样的 错误：输入字符串的格式不正确。错误行是行 lngCount = cmd.ExecuteScalar()，提示说明：InvalidCastException: 从字符串“zm”到类型“Integer”的强制转换无效。请问怎么具体改正？

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim ConnString As String
        Dim strSql As String
        Dim Conn As New OleDbConnection
        ConnString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source="
        ConnString += Server.MapPath("22.mdb")
        Conn.ConnectionString = ConnString
        Conn.Open()

        Dim cmd As New OleDbCommand
        Dim lngCount As Integer
        strSql = " select * from mima where 学号='" & txtUserName.Text & "'And 密码='" & Password.Text & "'"
        cmd.Connection = Conn
        cmd.CommandText = strSql
        lngCount = cmd.ExecuteScalar()
        If lngCount = "0" Then
            Response.Write("<script languaage='javascript'>alert('对不起！用户名和密码不符，请重新输入！')</script>")
            txtUserName.Text = ""
            Password.Text = ""
        Else
            Response.Redirect("http://www.163.com")

        End If
        cmd.Dispose()
        Conn.Close()
    End Sub