codice:
<%@ Page Language="VB" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<script runat="server">

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim d As DateTime = Nothing
        Dim result As Boolean = DateTime.TryParse(Me.TextBox1.Text, d)
        If result Then
            Me.div1.InnerText = d.ToString("d")

        Else
            Me.div1.InnerText = "Formato data sbagliato"
        End If
    End Sub
</script>

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Pagina senza titolo</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
        <div id="div1" runat="server"></div>
    </div>
    </form>
</body>
</html>