PHP: Send XML over POST with cURL and save response

gistfile1

function sendXmlOverPost($url, $xml) {
	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL, $url);

	// For xml, change the content-type.
	curl_setopt ($ch, CURLOPT_HTTPHEADER, Array("Content-Type: text/xml"));

	curl_setopt($ch, CURLOPT_POST, 1);
	curl_setopt($ch, CURLOPT_POSTFIELDS, $xml);

	curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); // ask for results to be returned

	// Send to remote and return data to caller.
	$result = curl_exec($ch);
	curl_close($ch);
	return $result;
}

I'm getting an "Array to string conversion" error for line 9. I'm sure it's a good xml file though.

What can I do to debug this?

Thanks for any help.