code behind page doesn't recognize html controls

 I have a web form that contains a SELECT dropdown box that I want populated with data from my sql server database.  On my code behind page, I am getting errors that say "name 'CaseIDs" not declared.  But CaseIDs is the SELECT box that I have on the aspx page.

 My aspx code looks like this:
 
1 <%@ Page Language="vb" AutoEventWireup="false" CodeBehind="Default.aspx.vb" Inherits="XMLGenerator._Default" %>
2
3 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
4
5 <html xmlns="http://www.w3.org/1999/xhtml ...