Maintain the state of dynamically added user control on postback?

I have a user control that contains only a text box and on another form I add this user control dynamically, a user can add the user control many times. I use a session variable to recreate the user control (maybe this approach doesn’t sound cool). After recreating the control the value of the textbox disappears, obviously. Is there any solution to maintain the state of the user control on postback?

“Cannot unregister UpdatePanel with ID ‘xxx’ since it was not registered with the ScriptManager… ” in RadGrid while editing record

Let me cut to the chase. My scenario is as follows: I have custom added fields to filter the RadGrid and filtering works perfectly. The problem comes when I want to edit record using EditForm inside RadGrid. It used to work fine, but then I had some problems with selecting the right row (I was always getting the wrong row selected) so this is what I did to fix it.