Hi
try this example to validate ListBox control using CustomValidator Control
<script type="text/javascript">
function ValidarListaSeleccionada(sender, args)
{
args.IsValid = document.getElementById(sender.controltovalidate).options.length>0;
}
</script>
<div>
<asp:ListBox ID="ListBox1" runat="server">
</asp:ListBox>
<br />
<asp:CustomValidator ID="CustomValidator1" runat="server" ClientValidationFunction="ValidarListaSeleccionada" OnServerValidate="CustomValidator1_ServerValidate" ControlToValidate="ListBox1" ErrorMessage="Select One." ValidateEmptyText="True"></asp:CustomValidator><br />
<br />
<asp:Button ID="Button1" runat="server" Text="Send" />
</div>
And the server side function, just in case
protected void CustomValidator1_ServerValidate(object source, ServerValidateEventArgs args)
{
args.IsValid = lBox.Items.Count > 0;
}
Hope this helps
Good Luck
