In short, why not just do:
<select style="width: 140px" name="RptType" onchange="this.form.submit();">
<option selected>--choose one--</option>
When you omit the action= from a <form>, it submits the page back to itself.
You'd then change your ASP code to use
RadioValue1 = Request.Form("RptType")
And I just notice that you were doing
set RadioValue1 = Request.Form("hdnType")
NO! The set there is INCORRECT.
(And I also got rid of the invalid id='s in your <option> tags!)
(And since the value= in our <option>s were the same as the text, the value= was also unnecessary.)
(Finally, ONCHANGE only triggers is the user *MAKES* a change, which means that with your code the user would never trigger and "Overall" selection. So I changed the default <option> so a user can choose "Overall".)