Please Help - Update Xml threw PHP not Working

[ragazzo]

I really don't understand what is wrong. ` When I run the code I get error that reads "Catchable fatal error: Argument 1 passed to DOMNode::appendChild() must be an instance of DOMNode, null given in /home/a2489440/public_html/playlistaction.php on line 39" I don't quite know what that means can someone please help me? Thanks in advance and here is the url where I am attempting to use this code.