GetObject fails with Stellar MLS

[OwenWilliamConsulting]

Attempting to issue the following request to Stellar MLS:

$objects = $retsSession->GetObject('Property', 'ExtraLargePhoto', '1329630', '*', 1);

Error thrown is:

Warning: SimpleXMLElement::__construct(): Entity: line 1: parser error : Start tag expected, '<' not found in D:\Development\PHP\RETSDownloader\vendor\troydavisson\phrets\src\Http\Response.php on line 32

It looks like the first entry in the response is missing the XML header. Is there a configuration setting I need to add in order for that not to happen, or is it an issue with the Stellar RETS server itself sending back incorrectly formatted XML?