The Bug,
Create an ASP.net application
on a form insert a System.Web.UI.HtmlControls.HtmlTable
inside it insert a field required validator and a textbox, set the
validator's control to validate to the text box.
put a button on the page not inside the table.
on page load set the table's visible property to false
on button click set the tables visible property to true.

You will get the following error when you click the button
"Unable to find script library
'/aspnet_client/system_web/1_1_4322/WebUIValidation.js'. Try placing this
file manually, or reinstall by running 'aspnet_regiis -c'.

you can solve this problem by manually inserting the following code line
into your aspx header.
<script language="javascript" type="text/javascript"
src="/aspnet_client/system_web/1_1_4322/WebUIValidation.js"></script>

I don't understand why Microsoft hasn't released any updates for Visual
Studio.NET in the past 2 years.  I have run into a lot of little annoying
bugs that should be fixed.