using a script to download images of graphs

I would like to have a script download the graphs nagiosgrapher produces into files. I would like to incorporate those files into an email and send it off everyday.

I am using a php script to emulate the links that are provided by nagiosgrapher for the png filetype on a graph. That link includes a number of posted variables to allow the cgi script to make the graph. I get a png file created with the following error on it;

RRD Error: start time: unparsable time:

Here is the link that I am attempting to emulate from the live webpage;

https://itinventory.alderfer.local/cgi-bin/nagios3/rrd2-system.cgi?host=temptrax;service=Quick_Chill;width=720;height=250;type=AVERAGE;title=1 Current;start=-21600;end=1327617467;imageformat=png

Here is a listing of the code I have to emulate that link:

#!/usr/bin/php
<?php
$ch = curl_init();
$right_now=time();
$fields = array(
 'host'=>urlencode('temptrax'),
 'service'=>urlencode('Main_Warehouse'),
 'width'=>urlencode('720'),
 'height'=>urlencode('250'),
 'type'=>urlencode('AVERAGE'),
 'title'=>urlencode('1 Current'),
 'start'=>urlencode(-21600),
 'end'=>urlencode($right_now),
 'imageformat'=>urlencode('png')
 );
$url="https://itinventory.alderfer.local/cgi-bin/nagios3/rrd2-system.cgi";

$fp = fopen("test.png", "w");

curl_setopt($ch,CURLOPT_URL,$url);
curl_setopt($ch, CURLOPT_FILE, $fp);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER,"FALSE");
curl_setopt($ch, CURLOPT_USERPWD, "guest:");
curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);

$results=curl_exec($ch);

fclose($fp);
?>

I have tried many different forms of start time to see if the error would at least change, but it does not. I found a few items on the web that sugest the it might be a php variable issue, specifically register_globals needs to be off. It is, but that does not seem to be my problem.