validation doesn't work sometimes

[Shane]

I've got a C# ASP.NET web form that fails to validate
under certain conditions. I have a radio button that
causes an AutoPostback that enables certain other elements
on the form. If I click that radio button, the validation
will work when I click Submit. However, if I enter the
page and never click that radio button then the page
submits as if there were no validation at all. I'm not
sure how that radio button fits into the picture but was
wondering if anyone else had seem something similar to
this?

Thanks in advance for any helpful ideas anyone may have.
Shane