php output explanation

Hello experts.
I'm using the swfupload plugin (http://demo.swfupload.org/v220/index.htm).I'm using coldfusion server language and unfortunately i get the error:500 using my cfm upload page.
Testing with upload.php page (look below) i have no errors.
Can you please explain what the php page is returning or what is the output so that i can find where the problem is?

<?php
	if (isset($_POST["PHPSESSID"])) {
		session_id($_POST["PHPSESSID"]);
	}
	session_start();

	// The Demos don't save files


	// In this demo we trigger the uploadError event in SWFUpload by returning a status code other than 200 (which is the default returned by PHP)
	if (!isset($_FILES["Filedata"]) || !is_uploaded_file($_FILES["Filedata"]["tmp_name"]) || $_FILES["Filedata"]["error"] != 0) {
		// Usually we'll only get an invalid upload if our PHP.INI upload sizes are smaller than the size of the file we allowed
		// to be uploaded.
		header("HTTP/1.1 500 File Upload Error");
		if (isset($_FILES["Filedata"])) {
			echo $_FILES["Filedata"]["error"];
		}
		exit(0);
	}
	
	echo "Make sure Flash Player on OS X works";
?>

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