I am trying to create a drilldown that will show the daily numbers from a 3D column chart that shows monthly totals. I'm using the dataURL method to create the 3D column chart. My chart container page is called wordform.php; my data provider page is called BuddyMonthlyData.php. I have created a second data provider page called BuddyHistoryData.php and tested to see that the sql works correctly.I changed addDataFromDatabase in BuddyMonthly Data to this --
$FC->addDataFromDatabase($result, "total", "months","","BuddyHistoryData.php?month_name=##months##");
When I click on a column I can see the correct value for the month is being passed to the new page (it shows in the address bar) but the only thing that displays is the word Chart, centered at the top of the page. What am I doing wrong? 
I've pasted BuddyHistoryData.php below.
<?php
session_start();
include("includes/WCBConn.php");
include("includes/FusionCharts_Gen.php");
//This page generates the XML data for the Pie Chart contained in
//Default.php.
//For the sake of ease, we've used an MySQL databases containing two
//tables..
//Connect to the Database
$link = connectToDB();
# Request the month name from QueryString, we set the MonthName in BuddyMonthlyData.php
$MonthName = $_REQUEST['month_name'];
# Create a column 2D chart object
$FC = new FusionCharts("Column2D","650","450");
# Set Relative Path of swf file.
$FC->setSwfPath("includes/");
#store chart attributes in a variable
$strParam="caption=Average and Word Count;
showBorder=1;showwritten=1;formatNumberScale=0;decimalPrecision=0;rotatenames=1;
linecolor=8F3844;outCnvBaseFontSze=12;outCnvBaseFontColor=3D515C";
#Set chart attributes
$FC->setChartParams($strParam);
// Fetch all user records using SQL Query
//Store chart data values in 'total' column/field and category names in 'written_date'
$strQuery = "select name, date_format(written_date, '%b %e')as written, words as total, written_date as sortdate
from buddies
where name = '$_SESSION[sess_name]'
and date_format(last_day(written_date),'%b')='" . $MonthName . "'
union select name, date_format(day, '%b %e') as written, words as total, day as sortdate
from wallofshame
where name = '$_SESSION[sess_name]'
and date_format(last_day(day),'%b')='" . $MonthName . "'
order by sortdate";
$result = mysql_query($strQuery) or die(mysql_error());
// echo "value of result is " . $result;
//Pass the SQL Query result to the FusionCharts PHP Class function
//along with field/column names that are storing chart values and corresponding category names
//to set chart data from database
if ($result) {
$FC->addDataFromDatabase($result, "total", "written");
}
mysql_close($link);
//Set Proper output content-type
// ***** if the line below is uncommented I get "Only one top level element is allowed" error *****
//header('Content-type: text/xml');
//Just write out the XML data
//NOTE THAT THIS PAGE DOESN'T CONTAIN ANY HTML TAG, WHATSOEVER
// print $FC->getXML();
$FC->renderChart();
?>