asp:listbox validation
<p>I have two asp:ListBox. The ID's are Authors and AuthorsSelected. Authors listbox is loaded with all  the authors and AuthorsSelected is empty at first. Using  Javascript code, I am moving items from Authors to AuthorsSelected.</p>

<p>Now, before submitting the form, I want to verify that AuthorsSelected listbox is not empty. I tried asp:RequiredFieldValidator and it's not workijng and giving error message.</p>

<p>Please let me know how to validate the AuthorsSelected listbox and make sure it's not empty before submitting the form. Thanks.</p>
