C# - ItextSharp Nested Table On Multiple Pages Causes NullReferenceException?

I am getting a NullReferenceException when the following code is executed. I have also noticed that the nested table appeared on a new page when I added in the code that wrote cells to the main table. It doesn't occur if I take out the two loops that write cells to the main table.

<%@ Page Title="" Language="C#" MasterPageFile="~/Main.master" %>
<%@ Import Namespace="iTextSharp.text" %>
<%@ Import Namespace="iTextSharp.text.pdf" %>
<%@ Import Namespace="System.IO" %>
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
Document doc = new Document(PageSize.LETTER);
// Here is some stuff needed to put the pdf into the users response stream

[Code]....