PHP error_log writes in one folder, not another - php

Question

I have a simple PHP script that writes errors to an error log file, and also prints part of the error to the screen.
I first developed it in my "sandbox" project inside Aptana Studio (but really, they're just directories) where it worked beautifully. However, when I copied it over to my "production project" (again, it's really just a different directory on the webserver), it no longer logs messages to the errorlog.log file. All permissions are the same, and in fact I made the script executable (it was not in the other directory), and gave the directory full permissions (chmod 777). The errorlog.log file already exists as an empty file and is writable, just as it was in the sandbox.
Here is the code:
<?php
/* logerrors.inc.php - Prints a "formatted" error message which will be displayed
* within a handler (i.e. the notification bar) on the front end and writes
* the error to a text log.
*/
date_default_timezone_set('America/New_York'); // Required to avoid errors.
define("LOG_LOCATION", "errorlog.log"); // The location of the log file
function writeError($error_string, $technical_info_string = ""){
$tech_log_entry = ""; // We should only log techinical information
// if it's provided
if($technical_info_string != ""){
$tech_log_entry = "\n- Technical Info Provided: ". $technical_info_string;
}
// Writes a log entry with full details.
error_log("[ERROR: ".date('Y-m-d H:i:s') . "]\n- Error Displayed: ". $error_string .
$tech_log_entry ."\n\n",
3, LOG_LOCATION);
echo "error: " . $error_string; // Emits the $error_string as output
exit();
}
?>
Interestingly, the echo command at the bottom of the script is working just fine, so it's obviously not erroring out on the error_log function. It just isn't working.
Any thoughts as to where to look next or what else could be causing this?