>>>>I have "moved" (copied) my VS 2005 project (.NET 2.0) to VS 2012. Now (in VS 2012) under .NET 4.0 the validation does not work. Strange is that I created a test aspx page with the same validation as in one of the application pages; and the validation works in the test page. But not in one of the pages of the application. So there must be something different.
>>>>
>>>>How do you troubleshoot the validation? Where in the debugger (if this is where I should look) I can see the validation?
>>>>
>>>>This is the segment of code of my validation:
>>>>

>>>>  <asp:textbox id="RequestorPhone" CssClass="FieldRW" MaxLength="14" Runat="server"></asp:textbox>
>>>>			<asp:requiredfieldvalidator id="rfvRequestorPhone" runat="server" CssClass="FieldLabel" ControlToValidate="RequestorPhone"
>>>>			ErrorMessage="RequiredFieldValidator" Enabled="True">  Please enter your telephone</asp:requiredfieldvalidator>  
>>>>        <asp:button id="Submit" Runat="server" Text="Submit" ></asp:button>  
>>>>

>>>
>>>Do you mean you don't see errors when you press Submit button? The above looks like server side validation, does the test page show errors right away (client side validation)?
>>
>>Yes, when I click on Submit the page, it is submitted and no error is shown. But I just added the controls (as shown above) as test to the application page with a test button. And when I click on Test Submit button, the error is shown and the page is not submitted. But when I click on the application "submit" button the page is submitted without a message. So on the same page I have an issue and don't have an issue. I will continue exploring.
>
>May be that Submit button doesn't do anything? Did you trace its Click event?

The Production Submit button does something and the results are shown. So Click works; it is just that no error is shown. That is, the page is not validated. The Test Submit does nothing but the error does show. This was the purpose of my question in this thread is to "how to debug the validation."