Va bene a patto di usare le virgolette semplici, come detto dal moderatore.
Comunque, copiato, incollato, sostituito quei caratteri con le virgolette e va

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

<script runat="server">
    Sub ChangeNames(obj As Object, e As EventArgs)
        If rlSex.SelectedIndex = 0 Then
            'femmina
            lbNames.Items(0).Text = "Sally"
            lbNames.Items(1).Text = "Sara"
            lbNames.Items(2).Text = "Hope"
            lbNames.Items(3).Text = "Kaylee"
        Else
            'maschio
            lbNames.Items(0).Text = "John"
            lbNames.Items(1).Text = "Chris"
            lbNames.Items(2).Text = "Daniel"
            lbNames.Items(3).Text = "Walter"
        End If
    End Sub

    Sub DisplayMessage(obj As Object, e As EventArgs)
        lblMessage.Text = obj.SelectedItem.Text & _
        " is a wonderful name!"
    End Sub
</script>
<html>
<body>
    <form id="Form1" runat="server">
    <asp:Label ID="lblMessage" runat="server" />


        Choose the sex of your baby:
        <asp:RadioButtonList ID="rlSex" runat="server" OnSelectedIndexChanged="ChangeNames" AutoPostBack="true">
            <asp:ListItem>Female</asp:ListItem>
            <asp:ListItem>Male</asp:ListItem>
        </asp:RadioButtonList>
        


            Possible names:

            <asp:ListBox ID="lbNames" runat="server" OnSelectedIndexChanged="DisplayMessage" AutoPostBack="true">
                <asp:ListItem></asp:ListItem>
                <asp:ListItem></asp:ListItem>
                <asp:ListItem></asp:ListItem>
                <asp:ListItem></asp:ListItem>
            </asp:ListBox>
            


    </form>
</body>
</html>