Data Paging and passing variables to text box

Hi,
 
Please help I am having troubles making the code run. I have a web page with a gridview and a checkbox. I would like the button when selected to pass the category id. I have managed to get it work without paging. Once the paging kicks in see below, I am unable to run the code. Please see below.
 
Thanks,
Nijojo.
 
 
In the design: ASPX
 
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="s ...