Ye check the messageboxes they are useless in deployment.
Now.If you do a postback on the page then you run this:
Me.RadioButtonList1.Items.Clear()
So you clear everything.How do you expect something to stay checked?
Remember doing a postback the second time does not mean that the page_load will not run.
Now if that is what you want from code then you can do something simple.Using session or viewstate you can save the checked value and after the postback you can pass it to your radiobutton.